The myth of normal river flow: Drought, floods, and management of California’s rivers

By Julie Zimmerman, Jennifer Carah, Kirk Klausmeyer, Bronwen Stanford, Monty Schmitt, Mia Van Docto, Mary Ann King, and Matt Clifford

Is California still experiencing drought? Even after a winter of record rainfall and snowpack, followed by a tropical storm, this is still an important question. And if you read the headlines, the answer is…yes and no. Although drought has been declared officially over, unsustainable groundwater pumping and overallocation of surface water leads to water deficits that persist, stressing rural communities, urban water supplies, and ecosystems. So even in this year of abundant rainfall and snowpack, water managers and river ecologists are still thinking about drought. In fact, drought conditions can be thought of as the base case, or the more common of two extremes that tend to drive management action in California. As climate change increases frequency and severity of both drought and flood in California (Swain et al. 2018), water managers must continuously plan for both very dry and very wet conditions.

What makes water management in California so challenging?

California’s patterns of rainfall and river flow are defined by variability and extreme events. Precipitation and streamflow in California are more variable from year-to-year and within a year than any other part of the U.S. (Dettinger 2011). The dry season can last for 6 months or more in many parts of California, with many rivers relying on groundwater to keep flowing, and species relying on the ability to migrate from drying rivers to survive. Freshwater species are adapted to natural variability in river flow, but not to the alterations in flow caused by people – including water extraction, river regulation from dams, and climate change. The vast majority of rivers in California experience altered flow conditions (Zimmerman et al. 2018) and human water use, management, and habitat loss have worsened drought conditions (AghaKouchak et al. 2015). Human activities have at least doubled the probability of occurrence of extreme drought compared to natural conditions (He et al. 2017). This pattern would only intensify if climate change were included in the analysis.

A result is that freshwater biodiversity is in crisis, in California and around the world. Declines in biodiversity in freshwater habitats are happening faster than any other habitat type. Freshwater covers less than 1% of the earth’s surface, but holds 10% of the earth’s species, including one-third of all vertebrates (Tickner et al. 2020). The Living Planet Index ( indicates population declines for freshwater species of 81% between 1970 and 2012, the greatest decline over all habitat types, with the main threats including habitat loss and degradation from dams and unsustainable water use. Freshwater biodiversity loss in California follows – or even leads – the global trend. In 2021, 73% of California’s freshwater fishes were extinct, listed under the Endangered Species Act, or considered species of special concern (Leidy and Moyle 2021). Beyond fishes, nearly half of California’s freshwater species are threatened with extinction, and that number is far higher – 90% for species found only in California and nowhere else on earth (Howard et al. 2015).

When are California rivers experiencing drought, and when is it a problem?

Here’s what we know: drought conditions are occurring with more frequency, greater severity, and longer duration. Human water use compounds the effects of drought, further stressing the state’s ecosystems and impacting farms, rural communities, and urban water supplies. Water use and management in California has become unsustainable in many watersheds, contributing to the drastic loss of freshwater biodiversity, decimating California’s iconic rivers, and triggering legal battles over a limited public resource with far too many demands. The problems are complex and overwhelming.

Where do we begin? One of our most critical needs is the ability to identify where drought conditions are likely, so that planning and action can occur in advance of the driest months and years. The U.S. Drought Monitor produces weekly maps of drought status based on precipitation, soil moisture, and other factors, as a way to determine drought impacts across the country – influencing agriculture, water supply, and terrestrial ecosystems. However, the U.S. Drought Monitor does not assess drought status in rivers and streams or potential drought effects on freshwater ecosystems. To fill this need, the Salmon and Steelhead Coalition, comprising The Nature Conservancy, Trout Unlimited, and California Trout, developed a Drought Flows Monitor web tool ( that identifies watersheds likely experiencing critically dry conditions. This tool can be used as a trigger to act quickly and efficiently to mitigate the effects of drought on freshwater species, regionally as well as in crucial watersheds. The Drought Flows Monitor can help guide decisions by identifying California watersheds with historically low natural flows where ecological risk from human water use is very high.

How does it work?

The Drought Flows Monitor relies on data in the Natural Flows Database (NFD) that can be accessed at The NFD models a range of natural stream flows for every stream reach in California at the monthly time step for 1950 to the present and is extended monthly. The most downstream reach of the largest river in each large watershed was selected to summarize statewide drought effects. Mean monthly natural flow predictions were downloaded from the NFD for each reach, and the likely presence of drought was assessed by comparing that monthly flow to the historical range of flows for that month and location. Drought severity was then characterized using U.S. Drought Monitor categories (

Categories include exceptional drought (lowest monthly flow for the model period); extreme drought (monthly flow in the 2-5th percentile of the range for the model period); severe drought (6-10th percentile); moderate drought (11-20th percentile); abnormally dry (21st-30th percentile) and average/ wet (31st-100th percentile). Figure 1 illustrates how the flow predictions for a given month and watershed are assigned to these categories.

Figure 1: Estimated unimpaired flow for July from 1950 to 2023 for Butte Creek. The lowest predicted flows are assigned a drought category and colored based on the percentile rank.

The tool can be used to look at historical and current drought conditions in California’s watersheds. Figure 2 shows drought status of California’s watersheds for the wettest (2017) and driest (1977) years from 1950 to 2022, according to the Northern Sierra 8 station index. One pattern is that drought conditions in 1977 were widespread and severe, but tended to be more widespread and severe in March and April than in August. This doesn’t mean conditions weren’t dry in August – streams were going dry and water was scarce – but three important insights can be gleaned from this pattern.

First, drought effects are not synonymous with dry streams. Abnormally low flows during the wet season are common during drought and can have big impacts even if a river doesn’t go dry. A river that might have 2,000 cfs in March of a wet year might only have 200 cfs in March of a drought year. That difference can have vast ecological consequences for species that rely on high flows to inundate rearing habitat and support migration in March.

Second, drought effects often appear in late winter and early spring and will likely persist until the start of the following year’s wet season. The reduction in August drought severity in 1977 shown in Figure 2 is likely because many streams have very low or no flows in August in most years, rather than because drought severity has lessened. Surface flow assessments can’t distinguish an average year from a drought year when flow is zero in both cases, even if impacts on riparian species and groundwater levels might be quite different. We know this because few areas of California are likely to get significant rain after April, and during dry years the end of significant storms often happens earlier, in March. Longer dry seasons are likely to become more common with climate change (Swain et al. 2018). We don’t have to wait until summer to start thinking about changing water management. We can confidently begin drought management actions much earlier, evaluating any rare late-season storms that may improve conditions.

Third, human and ecological experiences of a drought are based on observed flow – or what actually occurs in a river – rather than natural flow. These maps don’t include the effects of dams, diversions, or discharges. Streams often go dry during a drought because of the interaction of natural drought effects and human use – which is why human water use should be managed during drought years to avoid exacerbating drought effects that further degrade or dry up perennial streams and rivers.

Figure 2: Drought Flows Monitor results for the wettest and driest years during the 1950-2022 period according to the Northern Sierra 8 station index.

How can the Drought Flows Monitor improve water management decisions?

The Drought Flows Monitor captures current and historical drought conditions that occurred throughout California. Drought conditions can be detected for any month, but patterns of two or more months of drought by March or April result in drought conditions likely to persist until the start of the next wet season. This means we can tell fairly early in a year if water will get scarce during drier and hotter months.

At least two types of management decisions can be made using this information: 1) immediate water conservation efforts for priority streams and rivers as a watershed enters drought conditions, according to natural flow estimates, and 2) planning for longer-term drought actions over the dry season, once a watershed has been in drought conditions for two or more months by April. The drought categories in the Drought Flows Monitor provide a useful framework for tailoring drought actions as drought severity increases, potentially beginning with voluntary water conservation efforts in the abnormally dry category, and progressing to water restrictions or curtailments as watersheds enter severe, extreme, and exceptional drought. Advanced drought planning is lacking for most of California’s watersheds, but this tool provides data helpful in closing that gap, providing advance notice, and addressing water scarcity before it becomes an emergency.

What about human water use?

The Drought Flows Monitor only considers natural flow conditions, as an indicator of natural drought stress. It is not a comprehensive indicator of drought conditions experienced by freshwater species as it does not account for additional human modifications to flow and habitat. In some locations with long-term gages, results from the Drought Flows Monitor can be compared to gage data to confirm observed flow conditions are indeed critically dry, and identify locations where human water use is likely further stressing freshwater species. The Monitor includes links to USGS gages and visualizations of current flow observations compared with historical discharge to help users assess whether drought categories based on natural flows are consistent with observed data. But because gage locations are very limited, other approaches to assess actual flows and ecological stress are still needed. To help fill these data gaps, The Nature Conservancy is currently working with collaborators to model actual flows in all stream reaches in California, to provide a dataset of flows that include human modifications and can be compared with natural flow conditions and enable alteration assessments, even where gages are not present. You can learn about our work on actual flows modeling on the California Water Blog:

The Drought Flows Monitor can be used to trigger drought actions directly, and as a tool to identify watersheds to verify instream conditions and stress to freshwater species through site visits or collection of field data. Collection of site-specific data is resource-intensive and cannot be applied across large spatial scales; so, a hierarchical approach of identifying priority watersheds using the Drought Flows Monitor that are further assessed using site-specific empirical methods can help protect rivers across large areas. Used together, statewide assessment of drought severity using the Drought Flows Monitor, combined with empirical observations at targeted watersheds, can help guide decisions to protect freshwater species in the rivers and streams with the highest ecological risk of water use. That said, knowing actual flows is not necessary for action when drought conditions are expected. When a watershed experiences drought, any additional decrease in flow risks harm to freshwater species, and drought actions are warranted. The Drought Flow Monitor is a tool for developing more comprehensive management that is responsive to changing conditions, fast to implement, and widespread – the type of approach needed to protect freshwater biodiversity in a changing climate.

Julie Zimmerman is the Director of Freshwater Science for The Nature Conservancy’s California Chapter. Jennifer Carah is a Senior Scientist for The Nature Conservancy’s California Chapter. Kirk Klausmeyer is the Director of Data Science for The Nature Conservancy’s California Chapter. Bronwen Stanford is Lead River Scientist for The Nature Conservancy’s California Chapter. Monty Schmitt is a Senior Project Director for The Nature Conservancy’s California Chapter. Mia Van Docto is a Conservation Hydrologist for Trout Unlimited. Mary Ann King is the California Water Project Director for Trout Unlimited. Matt Clifford is the California Director of Law and Policy at Trout Unlimited.


The Drought Flows Monitor was developed by members of the Salmon and Steelhead Coalition Drought Science Workgroup, including: The Nature Conservancy (Julie Zimmerman, Jennifer Carah, Kirk Klausmeyer, Monty Schmitt, Jeanette Howard, Bronwen Stanford), Trout Unlimited (Matt Clifford, Mia van Docto), and California Trout (Gabe Rossi – also with UC Berkeley, and Charlie Schneider). The Coalition coordinated the development of this tool with the California Department of Fish and Wildlife Instream Flow Program.

Further Reading:

AghaKouchak, A., D. Feldman, M. Hoerling, T. Huxman, and J. Lund. 2015. Water and climate: Recognize anthropogenic drought. Nature 524: 409–411.

Dettinger, M. 2011. Climate change, atmospheric rivers and floods in California—a multimodel analysis of storm frequency and magnitude changes. Journal of the American Water Resources Association 47: 514–523.

He, X., Y. Wada, N. Wanders, and J. Sheffield. 2017. Intensification of hydrological drought in California by human water management. Geophysical Research Letters 44: 2016GL071665.

Howard, J. K., K. R. Klausmeyer, K. A. Fesenmyer, J. Furnish, T. Gardali, T. Grantham, J. V. E. Katz, S. Kupferberg, P. McIntyre, P. B. Moyle, P. R. Ode, R. Peek, R. M. Quiñones, A. C. Rehn, N. Santos, S. Schoenig, L. Serpa, J. D. Shedd, J. Slusark, J. H. Viers, A. Wright, and S. A. Morrison. 2015. Patterns of freshwater species richness, endemism, and vulnerability in California. PloS ONE 10: e0130710.

Leidy, R. A., and P. B. Moyle. 2021. Keeping up with the status of freshwater fishes: A California (USA) perspective. Conservation Science and Practice 3: e474.

Swain, D. L., B. Langenbrunner, and J. D. Neelin. 2018. Increasing precipitation volatility in twenty-first-century California. Nature Climate Change 8: 427–433.

Tickner, D., J. J. Opperman, R. Abell, M. Acreman, A. H. Arthington, S. E. Bunn, S. J. Cooke, J. Dalton, W. Darwall, G. Edwards, I. Harrison, K. Hughes, T. Jones, D. Leclère, A. J. Lynch, P. Leonard, M. E. McClain, D. Muruven, J. D. Olden, S. J. Ormerod, J. Robinson, R. E. Tharme, M. Thieme, K. Tockner, M. Wright, and L. Young. 2020. Bending the Curve of Global Freshwater Biodiversity Loss: An Emergency Recovery Plan. Bioscience 70: 330–342.

Zimmerman, J. K. H., D. M. Carlisle, J. T. May, K. R. Klausmeyer, T. E. Grantham, L. R. Brown, and J. K. Howard. 2018. Patterns and magnitude of flow alteration in California, USA. Freshwater Biology 63: 859–873.

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Evolution of Drought Response and Resilience in California’s Cities

By Erik Porse

Drought is a regular event in California. In recent decades, California has experienced five prolonged drought periods (1976-77, 1987-1992, 2007-09, 2011-16, 2020-22). Urban water agencies have responded with investments in supply and demand management measures, which have made California’s cities more resilient to drought effects. What motivated these investments?

Our current habits of water use in California’s cities are shaped by past policies and habits. Prior to 1976, urban water management in California was dominated by actions to increase supplies during the state’s Hydraulic Era (Hanak et al., 2011). In the early 1900’s, California’s developing cities built large infrastructure systems to transport water across long distances. San Francisco’s Hetch Hetchy Aqueduct (1913) and the Los Angeles Aqueduct (1914) were early projects. Later, in 1939, the Metropolitan Water District of Southern California completed the Colorado River Aqueduct. Importing water to increase local supplies remained the dominant approach through the 1970s with the completion of California’s State Water Project in 1972. These infrastructure projects grew metropolitan economies and allowed for high rates of water use in cities, which set a bar for perceptions of future efficiency (Cahill & Lund, 2013; Gleick et al., 2003).

By the late 1970s, the era of large engineering projects faded. Drought and land use changes in California instigated broader planning approaches. New sources of water were fewer. The severe drought of 1976–1977 in California spurred statewide actions to reduce demand and diversify supplies (DWR, 1978; Mitchell et al., 2017).[1] By 1977, an estimated 150 communities had implemented mandatory water conservation actions, especially in the San Francisco Bay Area and Sierra Foothills. Communities handed out water conservation kits, and some instituted fines (Agras et al., 1980; Morgan, 1982). Conservation was a public response to drought (DWR, 1978). Monthly water use reporting by agencies to the Department of Water Resources (DWR) through Bulletin 166, which started in 1960, was an important tool that evolved into the Public Water System Statistics (PWSS) after 1980 (it would take until 2013 for regular reporting of urban water use to again became widely and publicly available). In 1978, the California Energy Commission adopted efficiency regulations for toilets and faucets (Vickers, 2010). The regulations were early actions in what became decades of state and federal water efficiency measures (Diringer et al., 2018). After the drought subsided, studies evaluated economic impacts and effects on wastewater systems, while interest grew to understand how utilities could decrease demand (Berk et al., 1993; DeZellar & Maier, 1980; Koyasako, 1980).

Images of DWR’s Bulletin 166, which reported total and per capita urban water use for an example city (Sacramento) within the 1975 (left) and 1994 (right) updates to Bulletin 166 and the California Water Plan

California experienced another severe and prolonged drought from 1987-1992. By 1991, many urban water agencies had instituted conservation measures through water use restrictions, price surcharges, prohibitions on wasting water, public education programs, messaging, water use efficiency rebates, and giveaway programs, coupled by supply augmentation through trading (Dixon & Pint, 1996; Moore et al., 1993). Interest grew in recognizing and mitigating economic impacts of drought, spurred by a recession in 1990–1991 (Dixon & Pint, 1996). The drought solidified the types of activities that make up many of today’s utility conservation programs. In 1991, urban water agencies joined with advocacy groups to sign a joint Memorandum of Understanding (MOU) Regarding Urban Water Conservation in California and established the California Urban Water Conservation Council (CUWCC). CUWCC developed a suite of Best Management Practices (BMPs) that became a template for water conservation across the state (CUWCC, 1991). Shortly after, new federal requirements through the Energy Policy Act of 1992 increased efficiency for faucets, showerheads, and toilets (Diringer et al., 2018). Later, in 2007, the BMPs were adopted as a requirement to receive state funding (AWWA, 2017; Mitchell et al., 2017).

Changes in daily per capita demand for indoor water fixtures associated with year of installation. Sources: Compiled by OWP at Sacramento State (2022) based on studies from the Pacific Institute (Diringer et al., 2018), the Residential End-Uses of Water Study and the California Single-Family Water Use Efficiency Study (DeOreo et al., 2011, 2016), the Alliance for Water Efficiency (AWE, 2020), and the Handbook of Water Use Conservation (Vickers, 2010).

California endured another drought from 2007–2009. Many urban areas had limited effects, but broader water policy issues regarding water quality and pumping restrictions from the Southern Sacramento–San Joaquin Delta instigated statewide actions for urban water conservation (Mitchell et al., 2017). Senate Bill (SB) x7-7, the Water Conservation Act of  2009, required DWR to develop water use efficiency targets for agencies to achieve 20 percent savings by 2020 (DWR, 2010). Each agency was given a per capita target and had to submit data on recent demand. The targets established a contemporary baseline for future urban water use efficiency regulations. Requirements for submitting Urban Water Management Plans to DWR created new, openly available data. The SB x7-7 regulations also expanded consideration of Commercial, Industrial, and Institutional properties in conservation programs (DWR and CII Task Force, 2013). Yet, regular reporting of data on consumption remained intermittent and ceased after 2011.

Most Californians living in the state today experienced the 2012–2016 statewide drought. It was severe by comparison to the historical record (Griffin & Anchukaitis, 2014; Lund et al., 2018). The drought brought new policy approaches and, afterwards, a recognition of the potential severity of future conditions. Many urban areas relied on past investments and experienced limited effects in the first several years of drought (Lund et al., 2018). By 2014, California Governor Brown issued a voluntary water use reduction requirement of 20% across all urban areas through Executive Order B-17-2014. Water agencies implemented drought shortage contingency plans, which targeted savings of up to 20%, but through 2014, the Governor’s requested targets were only achieved in a few communities experiencing the most severe effects. In May 2015, with limited snowpack, agricultural fallowing, and drying wells in some small rural communities, the Governor signed Executive Order B-37-16, which required urban areas to reduce demand by 25%. The policy was later implemented with a sliding scale of conservation targets ranging from 4–36%, depending on past conservation actions taken by water agencies (SWB, 2015).

The mandatory restrictions were highly controversial. State regulatory agencies elicited input from water supply agencies, nonprofits, industry organizations, and researchers, which all shaped ultimate implementation of the executive order requirements (DWR, 2016; Mitchell et al., 2017; Talbot, 2019). By 2016, across the state, urban areas were meeting the statewide conservation target. They achieved this by boosting drought messaging and funding rebates to replace turf and indoor fixtures (Mitchell et al., 2017; Pincetl et al., 2019; Quesnel & Ajami, 2017). Municipalities and government agencies also reduced irrigation in public spaces. After the drought proclamation was lifted in 2017, water use increased but did not return to pre-2013 levels. The drought instigated significant legislation for urban water use, including SB 555 to require leak loss reduction programs and AB 1668-SB 606 to set supplier-specific urban water use targets for urban areas throughout the state.

After only a few years, drought conditions returned in 2020-2022. By Summer 2021, Governor Newsom urged urban residents to reduce water use by 15% through voluntary, but not mandatory requirements. California residents responded by reducing water use by 7%. Data collection and standardization efforts for urban water use reporting since 2013 made it easier to track savings. Most urban areas experienced limited effects, drawing on past investments in supply and efficiency measures. Yet, more widespread restrictions were looming if drought continued. For instance, in Spring 2022, parts of urban Los Angeles areas were under severe restrictions. While drought conditions eased in Winter 2022 and restrictions were lifted, without precipitation, the restrictions were set to expand. Widespread simultaneous drought across both California and the greater Colorado River Basin showed the vulnerability of California’s urban areas to severe 21st Century climate conditions. Significant policy changes from the 2020-22 drought are still emerging. For example, legislation to prohibit using potable water for irrigating ornamental (“non-functional”) turf in commercial, industrial, institutional, and multifamily properties may be enacted this year if signed by the Governor (AB 1572). The legislation was supported by major water agencies and emerged from drought response policies.

California’s cities today are better prepared to manage drought. This is the result of regulations, investments, collaboration, technology, and changes in our habits of water use. A severe and prolonged drought could still significantly impact urban areas, but most drought effects in cities today are slow to emerge and hard to evaluate (Lund et al., 2018). Wildfires amplified by drought disrupted urban life and imposed health risks in 2017-2020. Within cities, aging urban tree canopies, dominated by imported species with high water use needs, have suffered. Climate change adaptation for urban water management will increase costs for residents and businesses in California. Urban water agencies will need to improve outreach programs to support urban heat mitigation given changes in landscape irrigation. Finally, as cities have grown more efficient in how they use water, short-term options for future drought mitigation have reduced. Urban water agencies face significant challenges to support livable communities and contribute to climate change goals in California. The next chapter of drought response and resilience for California’s urban water sector is yet to be written.

Erik Porse is the Director of the California Institute for Water Resources and an Associate Cooperative Extension Specialist in the University of California Division of Agriculture and Natural Resources (UC ANR).

Further Reading

Agras, W. S., Jacob, R. G., & Lebedeck, M. (1980). The California drought: A quasi-experimental analysis of social policy. Journal of Applied Behavior Analysis, 13(4), 561–570.

AWE. (2020). AWE Conservation Tracking Tool, Version 3, Standard North American Edition. Developed by M-Cubed, for the Alliance for Water Efficiency (AWE).

AWWA. (2017). Errata to AWWA Manual M52, Water Conservation Programs—A Planning Manual , 2nd ed. (December 2017). American Water Works Association.

Berk, R. A., Schulman, D., McKeever, M., & Freeman, H. E. (1993). Measuring the impact of water conservation campaigns in California. Climatic Change, 24(3), 233–248.

Cahill, R., & Lund, J. (2013). Residential Water Conservation in Australia and California. Journal of Water Resources Planning and Management, 139(1), 117–121.

CUWCC. (1991). Memorandum of Understanding Regarding Urban Water Conservation in California. Amended January 4, 2016. California Urban Water Conservation Council.

DeOreo, W., Mayer, P., Martien, L., Hayden, M., Funk, A., Kramer-Duffield, M., Davis, R., Gleick, P., Heberger, M., Henderson, J., & Raucher, B. (2011). California Single-Family Water Use Efficiency Study. Aquacraft, Inc.

DeOreo, W., Mayer, P. W., Dziegielewski, B., & Kiefer, J. (2016). Residential end uses of water, version 2. Water Research Foundation.

DeZellar, J. T., & Maier, W. J. (1980). Effects of Water Conservation on Sanitary Sewers and Wastewater Treatment Plants. Journal (Water Pollution Control Federation), 52(1), Article 1. JSTOR.

Diringer, S., Cooley, H., Heberger, M., Phurisamban, R., Donnelly, K., Turner, A., McKibbin, J., & Dickinson, M. A. (2018). Integrating Water Efficiency into Long‐Term Demand Forecasting (4495). Water Reserach Foundation, Prepared by the Pacific Institute, the Institute for Sustainable Futures (University of Technology, Sydney), and the Alliance for Water Efficiency.

Dixon, L., & Pint, E. M. (1996). Drought Management Policies and Economic Effects on Urban Areas of California: 1987-1992 (Vol 813). RAND Corporation.

DWR. (1978). The 1976-1977 California Drought – A Review. California Department of Water Resources.

DWR. (2010). 20×2020 Water Conservation Plan. California Department of Water Resources.

DWR. (2016). Making Water Conservation a California Way of Life: Implementing Executive Order B-37-16. California Department of Water Resources, State Water Resources Control Board, California Public Utilities Commission, California Department of Food and Agriculture, and California Energy Commission.

DWR and CII Task Force. (2013). Commercial, Industrial, and Institutional Task Force Water Use Best Management Practices. Report to the Legislature. (Volume I: A Summary). California Department of Water Resources.

Gleick, P. H., Haasz, D., Henges-Jeck, C., Srinivasan, V., & Wolff, G. (2003). The Potential for Urban Water Conservation in California. 176.

Griffin, D., & Anchukaitis, K. J. (2014). How unusual is the 2012-2014 California drought? Geophysical Research Letters, 41(24), 9017–9023.

Hanak, E., Lund, J., Dinar, A., Gray, B., Howitt, R., Mount, J., Moyle, P., & Thompson, B. “Buzz.” (2011). Managing California’s water: From conflict to reconciliation. Public Policy Institute of California.

Kam, J., Stowers, K., & Kim, S. (2019). Monitoring of Drought Awareness from Google Trends: A Case Study of the 2011–17 California Drought. Weather, Climate, and Society, 11(2), 419–429.

Koyasako. (1980). Effects of Conservation on Wastewater Flow Reduction: A Perspective (EPA-600/2-80-137; p. 154 pages). U.S. Environmental Protection Agency Municipal Environmental Research Laboratory.

Lund, J., Medellin-Azuara, J., Durand, J., & Stone, K. (2018). Lessons from California’s 2012–2016 Drought. Journal of Water Resources Planning and Management, 144(10), Article 10.

Mitchell, D., Hanak, E., Baerenklau, K., Escriva-Bou, A., McCann, H., Perez-Urdiales, M., & Schwabe, K. (2017). Building Drought Resilience in California’s Cities and Suburbs. Public Policy Institute of California.

Moore, N. Y., Pint, E. M., & Dixon, L. S. (1993). Assessment of the economic impacts of California’s drought on urban areas: A research agenda. Rand.

Morgan, W. D. (1982). Water Conservation Kits: A Time Series Analysis of a Conservation Policy. Journal of the American Water Resources Association, 18(6), 1039–1042.

OWP at Sacramento State. (2022). Environmental and Economic Effects of Water Conservation Regulations in California: Evaluating effects of urban water use efficiency standards (AB 1668-SB 606) on urban retail water suppliers, wastewater management agencies, and urban landscapes. Prepared by the Office of Water Programs at Sacramento State, the University of California Los Angeles, the University of California Davis, and California Polytechnic University Humboldt.

Pincetl, S., Gillespie, T. W., Pataki, D. E., Porse, E., Jia, S., Kidera, E., Nobles, N., Rodriguez, J., & Choi, D. (2019). Evaluating the effects of turf-replacement programs in Los Angeles. Landscape and Urban Planning, 185, 210–221.

Quesnel, K. J., & Ajami, N. K. (2017). Changes in water consumption linked to heavy news media coverage of extreme climatic events. Science Advances, 3(10), e1700784.

SWB. (2015). State Water Board Adopts 25 Percent Mandatory Water Conservation Regulation. California State Water Resources Control Board.

Talbot, A. (2019). Urban Water Conservation in the Sacramento,California Region during the 2014-2016 Drought. University of California, Davis.

Vickers, A. (2010). Handbook of water use and conservation: [Homes, landscapes, businesses, industries, farms. Amy Vickers & Associates, Inc.

[1] Meteorological analysis identifies slightly different timeframes for several recent drought periods. See, for example, Kam (2019) that describes drought periods from 1975–1978 and from 1987–1994.

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Future Ancestors of Freshwater Fishes in California

By Peter B. Moyle

Smoky sunset over Eagle Lake, Lassen County, CA – home of endemic Eagle Lake rainbow trout and other endemic fishes and invertebrates. Sept 23, 2014. Will this terminal lake and its unique ecosystem survive global warming? This will be discussed in a future blog.

The Challenge

We are living in the Anthropocene, an era being defined by global mass extinctions caused by humanity. While on-going and impending extinctions of birds and other terrestrial vertebrates gain the most attention, the situation with freshwater fishes (and other freshwater organisms) is as bad or worse, partly because many freshwater extinctions are nearly invisible events, hidden by murky waters (Moyle and Leidy 2023). The extinction threat is especially high for obligatory freshwater fishes including many species endemic to California (Moyle and Leidy 2023). The ultimate cause is competition between people and fish for clean water. People are winning the competition at an accelerated rate, assisted by invasive species and global warming[1] and by the by continued expansion of the human population and its demands (Rypel 2023). The freshwater fish fauna of California is thus already on its way to becoming simplified and homogenized (Moyle and Mount 2007, Leidy and Moyle 2021).

The challenge, then, is how do we save some of the evolutionary lineages of native fishes to become the post-disaster ancestors of future fishes in the near (50-100 years) and long-term (100-1,000+ years)? This essay presents a rough proposal for answering this question. It is based on the assumption that it is desirable to save some evolutionary lineages of California’s native fishes to serve as ancestors of future fish species, for moral, aesthetic, and practical reasons. But volumes have been written about these reasons for saving ‘worthless’ species (see, for example, Marchetti and Moyle 2010, Rypel et al. 2021) so they, so they don’t need to be reiterated here. Suffice to say, the more fish species that are lost, the poorer the world’s freshwater ecosystems will be, as will the people that also depend on them today and in the future.


The Earth has undergone mass extinctions in the past. The best known is the asteroid-driven extinction at the end of the Cretaceous period, which may have coincided in part with massive volcanic eruptions. Interest in these events stems in part because they are regarded as the cause of extinction of the dinosaurs, allowing mammals, our ancestors, to dominate the world’s megafauna. Not much thought has been given to freshwater fishes that survived this disaster, even though streams in much of the world would likely have run high and muddy for hundreds if not thousands of years, until the stabilizing influence of trees and other terrestrial vegetation was renewed. Thus, the ancestors of most abundant and diverse group of freshwater fishes today, the Ostariophysi (carps, catfishes, characins) presumably survived the Cretaceous extinctions because of pre-adaptations for living in the murky waters flowing through a devastated landscape.

Mass extinctions have been caused by people in the past as well. The idea that people wiped out the megafauna of the lands they invaded as they moved from their ancestral home in Africa across the globe is now widely accepted. For example, Flannery (1994, 2015) described humanity’s ancestors as ‘Future Eaters’ because their consumption to extinction of large native mammals and birds resulted in major cascading changes to every ecosystem. This extinction seriously altered the native flora and fauna. In a way, modern extinctions are just a continuation of this human impact.

Now we are faced with increased frequency of disasters affecting humans and ecosystems resulting from, or exacerbated by, global warming. This reality has gripped the attention of many people, including scientists, politicians, and policy makers. But denial of global warming and its effects remains common, and despite climate disasters growing larger, more frequent, and more diverse. Millions of refugees worldwide are already seeking to survive outside their homelands, as their home areas become unlivable and/or dangerous due to droughts, floods, wars, disease, and a host of other problems. Such disasters are tragic symptoms of the declining planetary suitability of habitat for people, due in part, to population pressure exacerbated by global warming. This loss of habitat for people bodes poorly for fishes, especially those that require fresh water.

Characteristics of future ancestors

So, what freshwater fishes in California are likely to be good future ancestor material? What fishes can survive under the more likely and more pessimistic (realistic?) scenarios of a future in which most native freshwater fishes have been eliminated or close to it. Below are some examples, good and bad, of future ancestors. I assume here that large-scale moving of fishes of native fishes to new water bodies is neither practical nor desirable. I base the answer to the question on quantitative studies of characteristics of successful invasive fishes (Moyle and Marchetti 2006) and on vulnerability of California freshwater fishes to global warming (Moyle et al. 2013).

Ostariophysi. The Superorder Ostariophysi has major lineages worldwide in fresh water including carps, minnows (cyprinoids), catfishes, and characins. The fish of this superorder are usually among the most abundant fishes where found, with 11000+ species. They apparently were a minor part of the freshwater fauna at the time of the Cretaceous extinction event but survived to become dominant. There are many reasons for this but among them are likely a keen sense of hearing (Weberian ossicles), wide range of adult sizes, high fecundity, omnivory, high mobility, and high tolerance of poor water quality. These are all characters that would allow small populations to survive in devastated landscapes and to colonize new or recovering areas rapidly. So fishes such as common carp, various minnows, and catfishes could be likely ancestors for future freshwater fishes, worldwide. In California, sucker species (Catostomidae) and diverse cyprinoid fishes (Leuciscidae), such as Sacramento pikeminnow, hitch, chubs (Gila, Siphatales), and roach (Hesperoleucus) have the ostariophysan characteristics which may increase survival chances of at least some of the species.

Speckled dace in Lassen Creek, a tributary to Goose Lake, Modoc County. When Goose Lake has water, it develops large populations of dace and other native fishes. Photo by Thomas L. Taylor

Speckled Daces. The speckled daces are a lineage of ostariophysan native fishes (genus Rhinichthys) that seem ideally suited to become future ancestors. They were, until recently, regarded as one species, living in diverse habitats from British Columbia to Southern California and Mexico. In fact, “speckled dace” represents 15-20 isolated lineages (species and subspecies). Moyle et al. (2023) showed there are seven such lineages in California alone. They are remarkable because while genomics indicated that species-level populations have been separated for a million years or so, the separate populations are recognizably “speckled dace”; individuals from divergent populations cannot be readily told apart by people. Clearly the basic features of dace morphology and behavior are very conservative genetically and remained consistent over the 6+ million year history of this fish group. To achieve this broad distribution and diversity, these fish had to survive and thrive during long periods of changing conditions and dynamic geologic events, including periods of extreme drought and flood during the Pleistocene. Features that contribute to the survival all dace species, besides the basic ostariophysan characteristics, include (a) broad physiological tolerance, (b) small body size so large populations can continue in small waters, (c) flexible habitat requirements, and (d) ability to quickly colonize new or recovered waters. But even speckled dace may have a hard time persisting in isolated environments that are highly altered (e.g., Santa Ana speckled dace in the Los Angeles region).

Unlikely future ancestors. Some of today’s fishes, have a poor chance of being ancestors of future California fishes, if present trends continue. Many of these fishes are migratory species important in fisheries that that require large habitats (i.e., rivers, large lakes, estuaries) with relatively cold water (maximums <20° C for critical life stages). California fishes that qualify are sturgeons, all species of salmon and smelt, and most species currently listed as threatened or endangered under ESAs.

White and green sturgeon are fishes whose ancestors survived the Cretaceous extinction event(s) but presumably in ways opposite those of the Ostariophysans, by being large and highly mobile and by living for 100 years or more, with high fecundity. They also had a refuge in ocean waters. But both species are in danger of extinction in California, from multiple causes, as shown by the recent die-off in the San Francisco Estuary (Schreier et al. 2022). This reflects their increasing inability to live in human-dominated ecosystems. Their large size is no longer an advantage, unless northern rivers become more habitable for them.

Coho and Chinook salmon now depend on hatcheries for their survival in California; their future therefore is not secure. This is true for salmon in general at the southern end of their ranges; they are unlikely to make it to 2100 without human assistance (Lackey et al. 2006, Franks and Lackey 2015). Without a major change in human behavior, the future of salmon, at least as wild populations, is in Canada, Alaska, and Siberia (Rypel and Moyle 2023).

Endangered species. ESA-listed species already require intense care by people to persist, such as reproduction in hatcheries. Pupfishes, Colorado pikeminnow, and other desert fishes will survive without continual human assistance only if water is provided for them during extreme droughts, which is unlikely given water supply stresses in desert areas. Each listed species has its own challenges; the difficulty in overcoming these challenges is generally why they are listed and mostly not recovering. The challenges are only becoming harder to overcome.

Caveat. A problem I have largely ignored in this essay is that some of the most likely future ancestors in California waters are non-native fishes. Many are abundant and widespread, and have displaced native fishes. So they have already passed a suitability test of sorts, an ability to thrive in new, highly altered environments and an ability to become widely dispersed in their new homes, assisted by people. To make matters worse, invasive non-native fishes are often on the forefront as drivers of extinctions, a one-two punch with global warming (Moyle 2020, 2021). Examples of likely ancestors of future California fishes include Mississippi silverside, common carp, western mosquitofish, largemouth bass, and tilapia species.

Taking Action

People have had short but highly damaging impacts on most of this planet’s inhabitants, and the immediate future looks to be one in which effective collective action seems unlikely. We can therefore expect the current global extinction event to only accelerate; fishes will disappear as fast or faster than terrestrial vertebrates. The event will be recorded geologically as having taking place in the blink of an eye. But some animals and plants will survive. These will be the future ancestors. How can we maximize the pool of future ancestors in California, under the supposition that the more lineages that survive, the more diverse future lineages will be available to adapt to the changed world? This would seem to be desirable if more people choose to become a benign part of the Earth’s ecosystems and that diverse fishes are part of those ecosystems. While unlikely, in California, a start in this direction would be to establish Freshwater Protected Areas under the state’s 30×30 Initiative. See also Moyle 2002, Moyle et al. 2020, Rypel 2023.

Establishing a system of Freshwater Protected Areas now, as part of the 30×30 Initiative, would be a major step for aquatic conservation in California. Such a system should encompass California freshwater fish fauna, and other endemic aquatic biota. There will be tendency, of course, to give habitat for ESA-listed species a priority. But many of these species are or will become conservation dependent, requiring interventions of various sorts (e.g. hatcheries) even if habitat is provided (e.g., delta smelt). They have a low probability of surviving under most likely scenarios described previously. A preponderance of native fishes already are listed under ESAs or considered to be in decline (species of special concern). These fishes have an increasingly high probability of going extinct as long habitat alteration continues and severe droughts alternate with extreme floods, driven by global warming and human unwillingness to make sacrifices necessary to reverse global warming.

Deer Creek, Tehama County, showing middle (left) and lower (right) reaches . This entire watershed is a good candidate for a Freshwater Protected Area that supports potential future ancestors of native fishes. Photos by author.

The best chance for listed species is probably to be part of clusters of species that have high potential for future ancestor-hood. These species would have to be managed as a unit within their natural habitat. In the Sacramento River watershed the ancestor species, all unlisted, could include: tule perch, prickly sculpin, hardhead, speckled dace, California roach, Sacramento sucker, Sacramento pikeminnow, and rainbow trout. The ideal place to conserve these fish could be undammed streams and their watersheds, such as Deer, Mill and Antelope creeks in Tehama County or the Fall River in Shasta County. In the Klamath region, special status and protection of habitat could be given to the combined Shasta, Scott, and Salmon rivers, as well as the connecting Klamath River in the region. Other possibilities include Goose Lake and its watershed, the Eel River and its watershed, the San Gabriel River and adjoining watersheds in Southern California, and the Owens-Death Valley region including Owens Lake.

While moving fish to other watersheds (assisted migration) is usually not a good idea, the Eel River is an intriguing example of where it seems to be working because the Eel now supports populations of Sacramento pikeminnow, coastal roach, and Klamath speckled dace, introduced from adjacent watersheds. However, the negative effects of these ‘native’ introduce d species on Eel River native fishes, especially salmonids, and invertebrates may outweigh the positive effects of establishing new populations. But the three species do have an increased probability of becoming future ancestors as a result.

The initial steps for future ancestor conservation would be to improve the habitat where needed and make selected watersheds as disaster-proof as possible. This could be done, for example, by intense forest and fire management, by reducing road impacts, by improving floodable areas (e.g., bypasses and wetlands) and by generally creating a system that provides habitats that can persist though decades of droughts and floods. Ideally, there would be monitoring and management by local people who are committed to protecting the watershed and its biota.

Essentially, the idea is to treat Freshwater Protected Areas as habitat for future ancestors much as you would critical habitat for ESA-listed species, only for multiple species. However, if the global climate disaster becomes as severe as some speculate, refuges for future ancestors should be able to persist on their own, with little or no human management, for a long time: decades, perhaps hundreds of years.


If you think the idea selecting and protecting future ancestors is laughable, think of what the world will be like in the next 50-100 years if present trends continue, including increasing temperatures. If changes in climate are denied, then it seems silly to deny related changes in ecosystems that are affected by global warming. Currently, most sacrifices needed to reduce the impact of global warming are being rejected, ignored, or minimized. The oceans will be much warmer, so coral reefs and other marine ecosystems will likely be reduced or eliminated, as will most oceanic fisheries. Warmer oceans will be tied to floods and droughts at a world scale, with larger storms, challenging infrastructure such as levees and dams. More people will become climate refugees, with fewer safe places to go. In such scenarios, future ancestors of any creature but humans will receive little consideration. Species will survive to become ancestors mostly by chance, being lucky enough to survive in an unplanned refuge or being capable of surviving in a devastated landscape (cockroaches, rats, and maybe mosquitofish). But perhaps we can increase chances of survival for diverse lineages, including fishes, by creating some refuges now, as a gift to the future.

I hope this vision of the future is overly pessimistic and that California’s leadership in combating global warming, protecting natural areas, and saving endangered fishes (and other species) will continue. We need to keep working to protect California’s amazing natural heritage on the assumption that the global community will come to its senses and take the actions needed to halt, then reverse global warming.

Peter B. Moyle is a Distinguished Professor Emeritus at the University of California, Davis and is Associate Director of the Center for Watershed Sciences.

Further Reading:

Flannery, T.F. 1994. The Future Eaters: an Ecological History of the Australasian Lands and People. Reed: New Holland.

Flannery, T.F. 2015. The Eternal Frontier: an Ecological History of North America and its Peoples. Grove Press.

Franks, S.E. and R. T. Lackey. 2015. Forecasting the most likely status of wild salmon in the California Central Valley in 2100. San Francisco Estuary and Watershed Science13(1).

Grantham, T. E., and 10 others. 2017. Missing the boat on freshwater fish conservation in California. Conservation Letters 10:77-85

Howard, J.K, and 12 others. 2018. A freshwater conservation blueprint for California: prioritizing watersheds for freshwater biodiversity. Freshwater Science 37(2):417-431.

Kirsch, A. 2023.The End of Us. The Atlantic(January-February): 58-65.

Lackey, R.T., D. H. Lach. and S.I. Duncan. 2006. Salmon 2100:The Future of Wild Pacific Salmon. American Fisheries Society , Bethesda MD.

Leidy, R. L. and P. B. Moyle. 2021. Keeping up with the status of freshwater fishes: a California (USA) perspective. Conservation Science and Practice 3(8), e474. 10 pages.

Marchetti, M.P.and P.B. Moyle. 2010. Protecting Life on Earth: an Introduction to the Science of Conservation. Berkeley: University of California Press.

Mount, J., and 12 others. 2019. A Path Forward for California’s Freshwater Ecosystems. San Francisco: Public Policy Institute of California. 32 pp.

Moyle, P. B. 2002. Inland Fishes of California. Revised and Expanded. Berkeley: University of California Press. 502 pp.

Moyle, P.B., 2020. Living with aliens: nonnative fishes in the American Southwest. Pages 69-78 In D.L. Propst, J.E. Williams, K.R. Bestgen, and C.W. Hoagstrom, eds., Standing Between Life and Extinction: Ethics and Ecology of Conserving Aquatic Species in North American Deserts. Chicago: University of Chicago Press.

Moyle, P.B., J. Howard, and T. Grantham. 2020. Protecting California’s aquatic biodiversity in a time of crisis.

Moyle, P.B. 2021

Moyle, P.B. and M. P. Marchetti. 2006. Predicting invasion success: freshwater fishes in California as a model. Bioscience 56:515-524.[515:PISFFI]2.0.CO;2

Moyle, P.B. and J. Mount. 2007. Homogenous rivers, homogenous faunas. Proceedings, National Academy of Sciences 104: 5711-5712.

Moyle, P.B., J. D. Kiernan, P. K. Crain, and R. M. Quiñones. 2013.Climate change vulnerability of native and alien freshwater fishes of California: a systematic assessment approach. PLoS One.

Moyle, P.B., N. Buckmaster, N. and Su, Y. 2023. Taxonomy of the Speckled Dace species complex (Cypriniformes: Leuciscidae, Rhinichthys) in California, USA. Zootaxa 5249(5):501-539.

Moyle, P.B. and R.L. Leidy. 2023. Freshwater fishes: threatened species and threatened waters on a global scale. In N. Maclean, editor. The Living Planet: The Present State of the World’s Wildlife. Cambridge University Press.

Moyle, P.B. and R.L. Leidy. 2023. Endangered freshwater fishes: does California lead the world?

Obura, D. O. and 16 others. 2021. Integrate biodiversity targets from local to global levels. Science 373 (issue 6556): 746-748.

Rypel, A.L., P. Saffarinia, C.C. Vaughn, L. Nesper, K. O’Reilly, C.A. Parisek, M.L. Miller, P.B. Moyle, N.A. Fangue, M. Bell-Tilcock, D. Ayers, and S.R. David. 2021. Goodbye to “rough fish”: paradigm shift in the conservation of native fishes. Fisheries 46: 605-616 .

Rypel, A.L. 2023. Facing the dragon: California’s nasty ecological debts.

Rypel. A.L. 2023. Wetlands on the edge.

Rypel, A.L., and P.B. Moyle. 2023. Hatcheries alone cannot save species and fisheries

Saunders, D.L., J. J. Meeuwig, and A.C. Vincent. 2002. Freshwater protected areas: strategies for conservation. Conservation Biology 16(1): 30-41.

Schreier, A., P.B. Moyle, N.J. Demetras, S. Baird, D. Cocherell, N.A. Fangue, K. Sellheim, J. Walter, M. Johnston, S. Colborne, L.S. Lewis, and A.L. Rypel. 2022. White sturgeon: is an ancient survivor facing extinction in California? 

Tickner, D. et al. 2020. Bending the curve of global freshwater biodiversity loss: an emergency recovery plan. Bioscience 70(4): 330-342.

[1] Alternate labels are climate change, global harming, or global disaster creation. Global warming is preferred because it is the driver of other disasters lumped under the innocuous “climate change.”

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Hidden links between aquatic and terrestrial ecosystems: part 3 – Eel River

By Nicholas Wright

The South Fork Eel River runs through old-growth conifer forest. Photo credit-Mikey Weir, CalTrout.

This blog is the third and final of a three part series on ecological subsidies that appeared throughout summer ’23.

In California’s north coast, the Eel River winds its way through hills with shady slopes carpeted in lush ferns and towering redwoods and sunny ridges covered in brushy chaparral. The South Fork Eel River has been the site of extensive research by UC Berkeley professor Dr. Mary Power that has upended the traditional paradigm in ecology that trophic subsidies from forested watersheds shape river food webs, but subsidies from rivers are unimportant to forests. 

During spring, floating mats of bright green algae grow on top of the water in the river. Aquatic insects like caddisflies and mayflies lay their eggs inside these mats, which provide nutritious food and protection from predators to their young when they hatch. Populations of many different species of these insects will emerge into their terrestrial adult forms in synchrony and then fly away from their algal homes, creating trophic subsidies that flow from the river into the forest.

Dr. Power’s lab has documented just how abundant and diverse the insectivorous consumers of this cross-system subsidy really are. Filmy dome spiders, which weave complex webs to catch aerial insects, grow larger but build smaller webs closer to the river due to the high density of insects. Isotopic analyses show that even spiders whose webs are hundreds of meters from the river consume substantial amounts of river insects (Power et al 2004). Fast-moving wolf spiders, which chase their prey on foot, tracked down algal mats to consume the insects emerging directly from them. Western fence lizards and sagebrush lizards, both thought to be grassland species, were found to be 7x more abundant alongside the river than in meadows during the spring and summer (Power et al 2004). To test whether these densities were because lizards were seeking out insects emerging from the river, or simply trying to warm themselves on the rocks, the Power lab built “subsidy shields”- enclosures that reduced the fluxes of aquatic insect biomass by 70%. Lizards trapped in the enclosures grew 7x slower than lizards trapped in enclosures open to the insects, and lizards placed in open enclosures left those with a subsidy shield to move into enclosures without one (Sabo and Power 2002).

Insects are not the only animals with a terrestrial adult stage whose juveniles consume the algal mats. Pacific tree frog tadpoles from the Eel River were found to grow faster and metamorphose sooner when fed filamentous and epiphytic green algae (which make up the floating mats) than other food sources (Kupferberg 1994). These tadpoles metamorphose into frogs that hop into the damp forest and provide an aquatic trophic subsidy for garter snakes, raccoons, and herons that consume them. 

Aerial insectivores are far more mobile than spiders, lizards, or frogs, and therefore energetically connect rivers to their watersheds across larger spatial scales. Swallows, black phoebes, and six different species of bats consume insects emerging from the Eel River, snatching them out of the air or plucking them off the water’s surface. Using ultrasound detectors, researchers in the Power lab found bat density was the highest directly above the river, and dropped steadily within 50 meters of the banks, and then plateaued at a low density (Hagen and Sabo 2011). Across some transects, there were 30x more bats above the river than there were just 50 meters away! After bats are done with a night of hunting, they head to their day roosts – cavities in old trees and cracks in large boulders, typically many km from the river. In their roosts, bats excrete the insects they consumed, depositing river nutrients in the form of guano. This nitrogen guano is also a trophic subsidy, feeding insect detritivores and providing a potentially important source of nutrients for the nitrogen-limited old-growth conifer forest.

Animal species that connect the Eel River and its watershed. Top row species all have an aquatic larval stage and then terrestrial adult forms (from left): caddisfly larva, Pacific tree frog, mayfly adult. Middle row species are terrestrial riparian hunters that feed on insect subsidies from river: wolf spider, western fence lizard, filmy dome spider. Bottom row species are aerial hunters that feed above the river and then transfer nutrients deep into the forest: black phoebe, Yuma myotis, violet-green swallow.

Other species generate far more massive fluxes of nutrients from the water to the forest. After spending years feeding in the prey-rich ocean waters off California’s coast, fall-run Chinook Salmon and Coho Salmon return to the Eel River to spawn. After laying and fertilizing their eggs, the salmon die and their carcasses are washed ashore or dragged on land by predators like black bears, river otters, and eagles. As the nitrogen and phosphorus-rich tissues of the salmon decompose, nutrients enter the soil and are taken up by plants. An experiment conducted in Alaska found that riparian trees receiving nutrients from decomposing salmon grew significantly faster than trees growing along the opposite river bank where salmon carcasses were removed (Quinn et al 2018). In California’s coastal streams, returning adult salmon import ~10x more phosphorous into freshwater than exported into the ocean, creating a vital ecological conveyor belt of nutrients from the ocean to the rivers to the forest (Moore et al. 2011).


Trophic subsidies are complex, cross-system biotic interactions that we are still working to understand. Studying Chinook Salmon reveals the web of trophic subsidies connecting California’s freshwater ecosystems and their watersheds as salmon move through different habitats and stages of their life cycle. As juveniles they consume terrestrial nutrients and energy, preying on insects as parr and floodplain zooplankton as smolt. Then as they die, they return nutrients from water to land in their carcasses, a trophic subsidy all the way from the Pacific Ocean.

Cross-system aquatic-terrestrial trophic subsidies in the life cycle of California Chinook Salmon.

Conserving salmon requires conserving entire watersheds–not just the physical riverscapes but also the aquatic and terrestrial biodiversity on which they depend. California’s streams, lakes, forests, farms, and floodplains are ecologically intertwined in a network of trophic subsidies that transcend habitat boundaries. We must protect both aquatic and terrestrial ecosystems, and the trophic subsidies connecting them, if we are going to successfully conserve either.

Nicholas Wright is junior specialist in the Johnson-Jeffres research group. 

Further Reading:

Bastow, J.L., Sabo, J.L., Finlay, J.C., and Power, M.E. (2002) A basal aquatic-terrestrial trophic link in rivers: algal subsidies via shore-dwelling grasshoppers. Oecologia, 131, 261–268.

Hagen, E.M. and Sabo, J.L. (2011) A landscape perspective on bat foraging ecology along rivers: does channel confinement and insect availability influence the response of bats to aquatic resources in riverine landscapes? Oecologia, 166, 751–760.

Kupferberg, S.J., Marks, J.C., and Power, M.E. (1994) Effects of variation in natural algal and detrital diets on larval Anuran (Hyla regilla) life-history traits. Copeia, 2, 446-457.

Moore, J.W., Hayes, S.A., Duffy, W., Gallagher, S., Michel, C.J., and Wright, D. (2011) Nutrient fluxes and the recent collapse of coastal California salmon populations. Canadian Journal of Fisheries and Aquatic Science, 68(7).

Power, M.E., Rainey, W.E., Parker, M.S., Sabo, J.L., Smyth, A., Khandwala, S., Finlay, J.C., McNeely, F.C, Marsee, K., Anderson, C. (2004) River-to-watershed subsidies in an old-growth conifer forest. Polis, G.A., Power, M.E., and Huxel, G.R. (Ed). Food webs at the landscape level. 

Quinn, T.P, Helfield, J.M., Austin, C.S., Hovel, R.A., and Bunn, A.G. (2018) A multidecade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone. Ecology, 99(11), 2433-2441.

Sabo, J. L., and M. E., Power. River-watershed exchange: Effects of riverine subsidies on riparian lizards and their terrestrial prey. Ecology, 83(7), 2002, 1860–69.

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Wetlands on the Edge

By Andrew L. Rypel

Fig. 1. Coastal wetlands are the most valuable type of ecosystem on Earth. Photo showing the Bayland Nature Preserve near Palo Alto, California. Credit: Frank Chen/Getty Images.

It’s really easy to overlook and undervalue wetlands. Some are small or just don’t look very important. Others are enormous, and cause flooding issues for homeowners and growers. Some might even think wetlands are gross, worry about mosquitos and vector borne illness, or have never experienced what it’s like to be close to or inside of one. It’s uncommon to see a home or store positioned on a wetland (usually because it was drained), so perhaps they can also appear to be taking up valuable real estate better utilized for ‘human needs’.

Naturally, wetlands require water, which means they compete with humans for the acre-feet we so often discuss in California water. Yet according to Constanza et al. 1997, ecosystem services for wetlands, compared to all other ecosystem types, are the most valuable on Earth. On average, estuarine wetlands deliver $43,486/ha/y in services (adjusted to 2023), followed closely by freshwater wetlands at $37,292/ha/y. Historically, there were alot of both types of wetlands in California – somewhere in the neighborhood of 4 million acres, but at least 95% of these habitats have been eliminated. Thus, widespread loss in wetlands, both in California and at broader scales, signal huge misunderstandings regarding their importance. Failure to understand and protect wetlands dovetails with our twin inability to protect freshwater biodiversity, so much of which relies directly on these habitats (Rypel 2023).

Wetlands provide countless benefits for people and ecosystems. They are a giant and natural filtration system that not only improves water quality (Gilliam 1994; Verhoeven et al. 2006), but also water quantities, primarily via groundwater recharge (Van der Kamp and Hayashi 1998). Wetlands trap sediments, remove excess nutrients like nitrogen and phosphorus, and detoxifies other chemicals (Duffy and Kahara 2011; Mitsch et al. 2015). And of course, wetland ecosystems promote biodiversity at all scales (Denny 1994). This is especially true in California where most of our fragile biodiversity relies explicitly on wetlands (Fig.1, Brinson and Malvárez 2002; Leibowitz 2003; Zedler 1991; Katz et al. 2013). Alpine lakes and mountain meadows in the Sierra Nevada host native frog, toad, fish and salamander populations, along with native sedges, grasses, mosses, trees and flowering wetland plants (Fig. 2, Knapp et al. 2007; Parisek 2023). Wetlands are especially crucial in the Central Valley – a literal well of freshwater biodiversity in California. Here, floodplains are the key (Sommer et al. 2001; Katz et al. 2017; Jeffres et al. 2020; Rypel et al. 2022). We increasingly understand that these habitats once served as overwintering habitats for migratory birds (Bird et al. 2001; Elphick et al. 2010), and as rearing habitats for juvenile salmonids and other native fishes of the Central Valley (Oppermann et al. 2017). Herpetofauna, like the giant garter snake, still require this exact floodplain habitat that is now mostly destroyed (Nguyen et al. 2023); hence the snake is nearly destroyed. These same floodplains, managed the right way, protect our communities from floods, and can even be used during dry seasons for agriculture (Holmes et al. 2021; Torres et al. 2022). Increasingly, we will also turn to wetland rehabilitation as part of climate change adaptation and mitigation strategies, especially in the mountains as an effort to slow runoff that incresingly will fall as rain rather than snow. This is one reason why beavers, a species once broadly maligned, now are generating interest as a nature-based solution for adapting to climate change, and creating and enlarging the footprint of wetlands (Rypel 2022).

Fig. 2. Camassia quamash (Pursh). Photo credit: William & Wilma Follette 1992. Western Wetland Flora: Field Office Guide to Plant Species.

Yet not all wetlands are equal in terms of conservation impact (Barik et al. 2022). Therefore, a major challenge for conservation science will be prioritizing ecosystems and watersheds that provide ‘bang for the buck’. NGOs often excel at these kinds of tasks, and can leverage prioritization frameworks to translate science into action by restoring wetlands, bringing down deadbeat dams, lobbying on behalf of beavers or engaging in other positive activities. Yet to my knowledge, there is no statewide tool for prioritizing conservation management of California wetlands. Tools and working groups exist for certain kinds of wetland ecosystems (e.g. mountain meadows, floodplains etc), but a statewide effort largely remains lacking. This is unfortunate because it will directly hinder the ability for an important effort like the California 30×30 initiative to gain true success. For example, what good is conservation of 30% of California, if the land is of the wrong type (i.e., not enough wetlands)?

I recently reacquainted myself with some of the excellent watershed conservation efforts in Minnesota (Jacobson et al. 2016). Their effort is focused more on forest soils than wetlands per se, but I think it is a good example and heuristic for how to build a statewide watershed conservation program. The MN watershed program seems to be especially targeted at private forests that are at risk of development. Tacit in the approach is a broader expansion of the notion of wetlands – that traditional wetlands alone probably cannot remove enough sediments and nutrients when exposed to intensive development and agriculture. What is unique and exceptional to me about this work is that 1) it is statewide in scope; and 2) it focuses on deliberate science-based targets. For example, researchers observe that after 25% agricultural and urban land use, major increases in phosphorus are observed in waterways, substantially increasing the risk for harmful algal blooms, fish kills and poor freshwater habitat. Therefore, a good goal for watersheds in Minnesota is 75% protection. Furthermore, they developed a prioritization tool (Fig. 3). The value of the tool is that watersheds meeting the threshold can easily be identified, along with those near the benchmark, and those far away. Essentially, you can easily pick out watersheds where additional protection or restoration would have the most positive impact.

Fig. 3. Example of a statewide conservation prioritization schema. In Minnesota, many watersheds in the northern part of the state are well-protected. Watersheds in the southern part of the state are highly developed and can only hope for partial restoration. Watersheds in the middle and near north part of the state appear to have the highest odds for full restoration. From Jacobson et al. 2016.

You might be looking at this example thinking, “Well, those thresholds are totally unrealistic in California. Maybe in Minnesota, but certainly not California.” Yes, perhaps a 75% threshold is unrealistic in parts of California, but i) This is also true in Minnesota (see southern region of Fig. 3B); ii) We don’t know what a threshold might be in California. And iii) From a policy perspective, a California threshold goal can be whatever we collectively make it. California also has the benefit of agroecosystems, some of which provide surrogate ecological benefits. I would contend, that at this point, we know enough about the surrogate ecological benefits of rice fields (Katz et al. 2017; Jeffres et al. 2020; Holmes et al. 2021; Rypel et al. 2022), that under proper management, these habitats might not count against a wetland protection goal, but rather towards it. Similar incentive programs for waterfowl and migratory birds have existed for years, primarily through NRCS practice standards. Ultimately, the broader point is that all these details and California idiosyncrasies can be worked out using a parallel system adapted to be California-centric. And having such a tool will only increase our ability to be strategic and wise with limited funds and time. Other states have also put forward statewide wetland conservation strategies/tools, so there are many models from which to pick, examine, study and even blend.

During spring of this year, a US Supreme Court ruling, in Sackett vs EPA, dramatically reduced federal protections for wetlands, especially small wetlands throughout the US. The ruling made less noise in California because our state has more stringent laws that provide a backstop to the federal change. These enhanced California laws are the product federal, state, and local agency staff that engaged with wetland science 10-20 years prior, and foresaw the need to safe guard against a shifting and uncertain legal focus of the Clean Water Act in California. However, the new nationwide impacts of the Sackett decision were on full display this last week when the US EPA issued their final rule in response to Sackett, functionally amending the definition of protected waters of the US. The net impact is that wide swaths of wetlands previously protected are not protected anymore, and it will be up to the states to do the hard work of figuring out how to step in. Many of them won’t. I worry especially about biodiversity hotspots in regions that have a poor history of freshwater conservation and lots of valuable wetland real estate (e.g., southeastern USA). Over time, the ruling will brutally show how wetlands remain under constant jeopardy, and have now been sent on a march to the absolute edge and beyond. Despite their ecological and economic values, it simply remains far too expedient to harm, reduce and eliminate wetlands. But understanding is growing, and I see signs (e.g., in the movement to protect and recover beavers) that people and communities are standing up. Indeed we must all learn and teach to better understand wetlands, and rescue our valuable swamps back from the edge!

I wrote this blog mostly while sitting in front of this wetland. Photo by the author.

Further Reading:

Barik, S., G. K. Saha, and S. Mazumdar. 2022. Conservation prioritization through combined approach of umbrella species selection, occupancy estimation, habitat suitability and connectivity analysis of kingfisher: A study from an internationally important wetland complex (Ramsar site) in India. Ecological Informatics 72:101833.

Bird, J., G. Pettygrove, and J. M. Eadie. 2000. The impact of waterfowl foraging on the decomposition of rice straw: mutual benefits for rice growers and waterfowl. Journal of Applied Ecology 37:728-741.

Brinson, M. M., and A. I. Malvárez. 2002. Temperate freshwater wetlands: types, status, and threats. Environmental Conservation 29:115-133.

Costanza, R., R. d’Arge, R. De Groot, S. Farber, M. Grasso, B. Hannon, K. Limburg, S. Naeem, R. V. O’Neill, and J. Paruelo. 1997. The value of the world’s ecosystem services and natural capital. Nature 387:253-260.

Denny, P. 1994. Biodiversity and wetlands. Wetlands Ecology and Management 3:55-611.

Duffy, W. G., and S. N. Kahara. 2011. Wetland ecosystem services in California’s Central Valley and implications for the Wetland Reserve Program. Ecological Applications 21:S128-S134.

Elphick, C. S., O. Taft, and P. M. Lourenço. 2010. Management of rice fields for birds during the non-growing season. Waterbirds 33:181-192.

Gilliam, J. 1994. Riparian wetlands and water quality. Journal of Environmental Quality 23:896-900.

Holmes, E. J., P. Saffarinia, A. L. Rypel, M. N. Bell-Tilcock, J. V. Katz, and C. A. Jeffres. 2021. Reconciling fish and farms: Methods for managing California rice fields as salmon habitat. PLoS ONE 16:e0237686.

Jacobson, P. C., T. K. Cross, D. L. Dustin, and M. Duval. 2016. A fish habitat conservation framework for Minnesota lakes. Fisheries 41:302-317.

Jeffres, C. A., E. J. Holmes, T. R. Sommer, and J. V. Katz. 2020. Detrital food web contributes to aquatic ecosystem productivity and rapid salmon growth in a managed floodplain. PloS ONE 15:e0216019.

Katz, J., P. B. Moyle, R. M. Quiñones, J. Israel, and S. Purdy. 2013. Impending extinction of salmon, steelhead, and trout (Salmonidae) in California. Environmental Biology of Fishes 96:1169-1186.

Katz, J. V., C. Jeffres, J. L. Conrad, T. R. Sommer, J. Martinez, S. Brumbaugh, N. Corline, and P. B. Moyle. 2017. Floodplain farm fields provide novel rearing habitat for Chinook salmon. PloS ONE 12:e0177409.

Knapp, R. A., D. M. Boiano, and V. T. Vredenburg. 2007. Removal of nonnative fish results in population expansion of a declining amphibian (mountain yellow-legged frog, Rana muscosa). Biological Conservation 135:11-20.

Leibowitz, S. G. 2003. Isolated wetlands and their functions: an ecological perspective. Wetlands 23:517-531.

Mitsch, W. J., B. Bernal, and M. E. Hernandez. 2015. Ecosystem services of wetlands. Pages 1-4. Taylor & Francis.

Nguyen, A. M., B. D. Todd, and B. J. Halstead. 2023. Survival and establishment of captive‐reared and translocated giant gartersnakes after release. The Journal of Wildlife Management 87:e22374.

Opperman, J. J., P. B. Moyle, E. W. Larsen, J. L. Florsheim, and A. D. Manfree. 2017. Floodplains: Processes and management for ecosystem services. University of California Press.

Parisek, C.A. 2023. A “peak” into California’s alpine lakes and their food webs.

Rypel, A.L., P.B. Moyle, and J. Lund. 2021. A swiss cheese model for fish conservation in California.

Rypel, A.L., C.A. Parisek, J. Lund, A. Willis, P.B. Moyle, Yarnell, S., and K. Börk. 2020. What’s the dam problem with deadbeat dams?,

Rypel, A.L. 2022. Nature has solutions…What are they? And why do they matter?

Rypel, A.L., D.J. Alcott, P. Buttner, A. Wampler, J. Colby, P. Saffarinia. N. Fangue, and C.A. Jeffres. 2022. Rice and salmon, what a match!

Rypel, A.L. 2023. Facing the dragon: California’s nasty ecological debts.

Sommer, T., B. Harrell, M. Nobriga, R. Brown, P. Moyle, W. Kimmerer, and L. Schemel. 2001. California’s Yolo Bypass: Evidence that flood control can be compatible with fisheries, wetlands, wildlife, and agriculture. Fisheries 26:6-16.

Torres, F., M. Tilcock, A. Chu, and S. Yarnell. Five “F”unctions of the Central Valley floodplain

Van der Kamp, G., and M. Hayashi. 1998. The groundwater recharge function of small wetlands in the semi-arid northern prairies. Great Plains Research:39-56.

Verhoeven, J. T., B. Arheimer, C. Yin, and M. M. Hefting. 2006. Regional and global concerns over wetlands and water quality. Trends in Ecology & Evolution 21:96-103.

Zedler, J. B. 1991. The challenge of protecting endangered species habitat along the southern California coast. Coastal Management 19:35-53.×30,reduce%20in%2Dstream%20water%20temperatures.

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Portfolio Solutions for Water – Flood Management

by Jay Lund

*this is a repost of a blog originally published in March 2019.

The tweet below, shows slight (but still frightening) levee overtopping this week on Cache Creek, just north of Woodland, California.  It also illustrates the combined operations of flood preparation and response, with a simultaneous floodplain evacuation order.  Integrating a range of preparations and responses have made the Sacramento Valley much safer from floods.

One often hears, “If only we did X, we would solve this problem.”  Alas, effective solutions are rarely so simple or reliable.  Most robust solutions for problems involve a diverse and complementary portfolio of actions, developed over time.  When a set of diverse actions are carefully crafted to work together, they often provide more effective, adaptable, and reliable performance, at less expense that a single solution.

The Sacramento Valley’s flood management system is a good example where a portfolio of actions has greatly reduced flood damages and deaths, with relatively little management expense and attention in a highly flood-prone region.  This case also illustrates how the many individual flood management options presented in the table can be assembled into a diversified cost-effective strategy involving the many local, state, and federal parties concerned with floods.

flood portfolio

Portfolio strategies usually include actions which work in different ways over different times.  Flood management portfolios usually include actions that prevent flooding (such as levees) complemented by actions that reduce the need for more expensive flood prevention (such as flood evacuations).  Actions which protect areas from flood waters (often structural actions) are distinguished from actions that reduce vulnerability to damage and death if flooding occurs.  Levees, bypasses, and reservoirs are all designed and operated to support each other in the Sacramento Valley to reduce the extent of flooding.  Floodplain land management and flood warnings and evacuations have greatly reduced the property and people exposed to flooding.

Because most floods occur and pass quickly, most flood management is in preparing for floods and flood recovery, rather than in response during actual floods.  As with fire-fighting, elections, and war, flood management time is more than 99% preparation and recovery and less than 1% actions during flood events.  Pre-flood preparations to contain floods (with levees, reservoirs, and bypasses), reduce flood damage potential (with evacuations, building codes, insurance, and floodplain zoning), and prepare for rapid flood operations and evacuations (with education, warnings, and training) are crucial.  Making and coordinating investments, training, and education are all prominent before floods, making urgent flood operations more effective (and less panicked).  Post-flood response also can reduce flood damages and help prepare for the next flood.  There is always a next flood.

Portfolio solutions require overcoming some challenges, however.  Because portfolio solutions involve a range of actions usually controlled by different authorities and groups, they require more social and political organization than single-action silver-bullet solutions.  This can take time, motivation, and leadership to bring together.  But such diversification of responsibility for implementing portfolio can help spread expenses and provide useful perspectives of attention to details and effectiveness.  In flood management, local residents and land owners, local governments, regional governments, and state and federal agencies all specialize in different elements of regional flood management.  This specialization helps lower costs, increase attention to detail, and diversify political support.  This can lead to a mutually-reinforcing ecosystem of institutions that are collectively more effective at attending the problem and innovating than would a single larger bureaucracy.

It took decades for California’s Sacramento Valley to build its current flood management portfolio.  Even so, some flood problems remain.  Small towns and some rural industries remain vulnerable – and there is always vulnerability to bigger floods and infrastructure failures.  There will always be residual flood risks, as flood solutions are never perfect or complete.

Flood problems also change as the economy, population, social expectations, and now climate change.  We now see floodplains and flood bypasses are closely linked to California’s environmental solutions, bringing new objectives in our flood discussions. Portfolio solutions can often better incrementally adapt to change because of their supporting diversified institutional network and operational flexibility.

Successes with water problems (and other areas) often comes from developing or evolving portfolio solutions.  An integrated range of institutions supports this management, mixing the advantages of centralized and decentralized governance and finance to make more effective and adaptable solutions at less expense.  No single person or institution can usually solve such problems.

A series of blog post essays will explore the use and development of portfolio solutions for major water problems.  Successes and challenges will be discussed, as well as the problem of coordinating portfolios of actions across problems – such as managing a common water infrastructure for floods, water supply, and ecosystems – which traditionally have separate solution portfolios.

Further Reading

California Department of Water Resources, Central Valley Flood Protection Plan,

Gilbert F. White (1937), Notes on Flood Protection and Land-Use Planning, Journal of the American Institute of Planners, 3:3, 57-61, DOI: 10.1080/01944363708978728

Independent Forensic Team (2018). “Independent Forensic Team Report: Oroville Dam Spillway Incident”. January 5, (2018).

Jeffres, C.A.; Opperman, J.J.; Moyle, P.B. (2008), Ephemeral floodplain habitats provide best growth conditions for juvenile Chinook salmon in a California river. Environ. Biol. Fishes, 83, 449–458.

Kelley, R. (1989), Battling the Inland Sea; University of California Press: Berkeley, CA, USA.

Lund, J.R. (2012), “Flood Management in California,” Water, Vol. 4, pp. 157-169; doi:10.3390/w4010157.

Jay Lund is a Professor of Civil and Environmental Engineering at the University of California, Davis.

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Shell-shocking Details About Freshwater Mussel Reproduction

By Andrew L. Rypel, Miranda Bell Tilcock, and Christine A. Parisek

Fig 1. Mantle lure of the plain pocketbook (Lampsilis cardium), a freshwater mussel. Photo by Philippe Blais,

One of our favorite aspects of teaching is (occasionally) being able to really surprise a student. Many of the fun nature facts folks pick up nowadays come from TV, YouTube, social media, and other media outlets. But these outlets have an inherent bias: they focus on the charismatic species. That is, the species that are big, fluffy, and widely adored. Yet there are so many fascinating species and ecology in the lesser appreciated taxonomic groups (not to mention, focusing on charismatic species leads to inequitable conservation – Rypel et al. 2021). And often, learning about these overlooked species can really blow the mind! Today, we’d like to introduce you all to the fascinating reproductive behavior of freshwater mussels.

Fig. 2. (Left) Vintage shell buttons from the White River, Indiana. Photo from (Right) Button cutters pose with a pile of shells outside a button factory circa 1919. Photo from U.S.Bureau of Fisheries and downloaded from

Freshwater mussels are fascinating creatures and are spectacularly underhyped. Their ecology and conservation status has been communicated previously on this blog. These animals are long-lived (up to 100 years old or more, Haag and Rypel 2011), are filter feeders, and are widely regarded as sentinels of outstanding water quality in freshwater ecosystems (Vaughn 2018). Some estimate that a single adult mussel can filter ~15 gallons of water per day! Mussels are also highly endangered; 73% of freshwater mussel species in North America are at risk of extinction (Williams et al. 1993). Causes for their decline are multifold, but include severe declines in water quality, fragmentation of rivers by dams, invasive species, overharvest from the pearl and button industries (Fig. 2), and climate change. A final, somewhat mussel-specific cause for their decline can also be the loss of their host fishes.

Fig. 3. Schematic of the life-history of freshwater mussels, from Hewitt et al. 2021.

Wait… did you say “host fishes”?! Yes indeed. Almost all species of freshwater mussels (unlike marine mussels) require fish hosts as juveniles. The glochidia (= baby mussels) attach primarily to the gills, but also the fins and skins of fishes. Here, they live off the blood of the fish host until large enough to fall off, hopefully into optimal habitat where they can become a big old mussel (Fig. 3). But, how then do the baby mussels actually get on the fishes? This is where the (al)lure of the mussel is perhaps most charming.

Many mussels have essentially evolved fishing lures (mantle lures) to attract fish hosts to the mussel (Fig. 1). A potential host fish will approach the lure, and if displayed convincingly enough, may ultimately bite the lure. But instead of getting a nutritious morsel of food, the fish instead gets a magazine of glochidia ejected into its face and mouth. The relationship these young mussels have with their host fish causes the fish some irritation but is not intended to harm the fish, as their main goal is to use the host fish for transport and dispersal (That’s one enterprising way to catch a Lyft!). Because certain species of mussels have evolved to use only certain species of fish, the mantle lures can be exceptionally specific, ornate, and tricky. Other mussel species are generalists, meaning they can use many species as hosts (including even some invertebrates). Below are a few examples of mantle lures in action, but we can also testify that YouTubing “mussel mantle lure” is a simple and effective way to waste a bit of time if you are so inclined.

The connectivity between freshwater mussels and fishes also means something for our ecosystems and their conservation. Put simply, freshwater mussel communities and freshwater fish communities are connected and literally feed off one another. In at least one case (Freshwater Drum, Aplodinotus grunniens), the fish can serve as a generalist host for at least a dozen or more mussel species in a single river. But drum also directly consume adult mussels as prey. In this way, drum literally farm their own food. Thus, the decline of mussels spells bad news for fishes, and vice versa. If native fishes decline, then there are no more hosts for the mussels.

The interestingness and diversity in nature brings joy to these authors’ lives, and hopefully also to yours. Over the years, we have introduced many students and community members to the wild reproductive behaviors of freshwater mussels. Only a handful are aware of this biology. This motivated us to write this blog and share it with all of you. It also gives us pause for how we are so rapidly modifying our ecosystems and losing species. Are we even aware of what we are losing? The more we study nature and ecosystems, the more it seems as though we are largely unaware of what’s being erased. This is sad for our planet, our species, and future generations that might not grow up ever encountering a legitimate, healthy mussel bed, or perhaps even a healthy river. But it’s also never too late to turn it around. To do this we will need broader awareness concerning the plight of all species, including the non-charismatic ones, along with the determination and patience to adequately protect them.

“The more clearly we can focus our attention on the wonders and realities of the universe about us, the less taste we shall have for destruction.” ~Rachel Carson, Silent Spring

Fig. 4. The Upper Truckee River has, until recently, been a stronghold for western pearlshell mussels (Margaritifera falcata); however the species has declined in this system, and across its native range. Photo from

Andrew L. Rypel is a professor of Wildlife, Fish & Conservation Biology and Director of the Center for Watershed Sciences at the University of California, Davis. Miranda Bell Tilcock is an Assistant Specialist at the Center for Watershed Sciences. Christine Parisek is a Ph.D. candidate in the Graduate Group in Ecology at UC Davis and a science communications fellow at the Center for Watershed Sciences.

Further Reading

Howard, J.K., J.L. Furnish, J.B. Box, and S. Jepsen. 2015. The decline of native freshwater mussels (Bivalvia: Unionidae) in California as determined from historical and current surveys. California Fish and Game 101: 8-23.

Haag, W.R., and A.L. Rypel. 2011. Growth and longevity in freshwater mussels: evolutionary and conservation implications. Biological Reviews 86: 225-247.

Hewitt, T.L., A.E. Hoponski, and D.O. Foighil. 2021. Evolution of diverse host infection mechanisms delineates an adaptive radiation of lampsiline freshwater mussels centered on their larval ecology. PeerJ 9:e12287.

Lawrence, A.J., and A.L. Rypel. 2023. Will more wildfire and precipitation extremes mussel-out California’s freshwater streams?

Maine, A., C. Arango, and C. O’Brien. Host Fish Associations of the California Floater (Anodonta californiensis) in the Yakima River Basin, Washington. Northwest Science 90: 290-300.

Murphy, G. 1942. Relationship of the fresh-water mussel to trout in the Truckee River. California Fish and Game 28: 89-102.

Rypel, A.L. 2008. Field observations on the nocturnal mantle flap lure of Lampsilis teres. The American Malacological Bulletin 24: 97-100.

Rypel, A.L. 2020. Losing mussel mass – the silent extinction of freshwater mussels.

Rypel, A.L., P. Saffarinia, C.C. Vaughn, L. Nesper, K. O’Reilly, C.A. Parisek, M.L. Miller, P.B. Moyle, N.A. Fangue, M. Bell-Tilcock, D. Ayers, and S.R. David. 2021. Goodbye to “rough fish”: paradigm shift in the conservation of native fishes. Fisheries 46: 605-616 .

Rypel, A.L. 2022. Being patient and persistent with nature.

Vaughn, C.C. 2018. Ecosystem services provided by freshwater mussels. Hydrobiologia 810: 15-27. 

Williams, J.D. M.L. Warren, K.S. Cummings, J.L. Harris, and R.J. Neves. 1993. Conservation Status of Freshwater Mussels of the United States and Canada. Fisheries 18: 6-22.

America’s freshwater mussels are going extinct — Here’s why that sucks

The strange, savage life of a freshwater mussel

California floater mussel take fish for an epic joyride

Xerces Society: about freshwater mussels

True facts: mussels that catch fish

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Hidden links between aquatic and terrestrial ecosystems: part 2 – Sacramento River

By Nicholas Wright

Running through the Central Valley’s patchwork of yellow, green, and brown farmlands is the deep blue of California’s largest river–the Sacramento. Once a much wider river, meandering across the flat valley floor, the Sacramento has been straight-jacketed by steep earthen levees and confined to a more controlled channel. On either side of the river, where once would have stretched seasonal floodplains dotted with gnarled cottonwoods, shrubby willows, and dense tufts of tule grass, there’s now a vast expanse of rice fields. Around 95% of historic floodplain habitat in the Central Valley has been lost to draining and agricultural conversion. There are only a few pockets of floodplain still left in the valley, mostly in the flood bypasses–areas where water from the Sacramento River is intentionally diverted during high-flow years. When river water inundates these floodplains a sort of ecological magic happens.

Thousands of acres of flooded rice fields which will be drained into the Sacramento River to give migrating salmon a trophic subsidy. Photo credit–Mikey Weir, CalTrout

As the water spreads and slows, terrestrial plant matter is flooded and microbes in the water begin to break it down. This detrital decomposition forms the base of a heterotrophic food web that is extraordinarily productive, fueling the growth of incredible densities of zooplankton. A great diversity of fish species, including juvenile Chinook Salmon, move onto the floodplains to feed on the zooplankton and grow rapidly in the warmer, slow-moving waters (Jeffres et al 2022). The incredible productivity of floodplains is the exact reason why their loss has been so damaging to freshwater ecosystems. Today most of the Sacramento River offers slim pickings for hungry fish, leaving juvenile salmon migrating downstream badly short on food.

There is one exception to that trend though–a rare few stretches of river receive pulses of water draining off floodplains that are dense with zooplankton. Research has shown that in wet years when floodplains like the flood bypasses are inundated, juvenile salmon in the Central Valley have more food in their stomachs than in dry years (Sturrock et al 2022). But the flood bypasses are relatively small and the majority of fish in the Central Valley have no access to floodplains. And here is where the rice fields, surprisingly, offer a potentially huge conservation opportunity. 

In winter, rice fields are flooded to decompose rice stubble and provide habitat for waterfowl, forming a sort of surrogate floodplain habitat. If that turbid, food-rich rice field water was drained back into the river, could it provide hungry fish with a floodplain food web subsidy? To test that idea California Trout and the Dr. Rachel Johnson-Dr. Carson Jeffres research group at the UC Davis Center for Watershed Sciences partnered to implement a landscape-scale experiment seeking to answer an important question–could rice field floodplain food webs be harnessed as subsidies to provide food to salmon in rivers? Salmon enclosure cages were set in the Sacramento River above (as a control) and at one-mile intervals below an export drain pumping in rice field waters. The cages were set for almost two months and each week at each site during that period zooplankton abundance was sampled, all of the fish were measured, and a few salmon were removed for stomach content analysis.

The outlet drain pumps turbid, zooplankton-rich water from the agricultural canal into the food-scarce Sacramento River. Photo credit–Bryce Craig at Pusher, Inc

The results of this study told a simple but powerful story. We found that all sites receiving the rice field subsidy had more zooplankton than the upstream site, but that zooplankton densities diminished at the sites further downstream from the export drain. We also found that the upstream salmon almost exclusively ate insects, like chironomids, while the salmon at the export drain almost exclusively ate zooplankton (CalTrout 2021). Even at the furthest site, six miles downstream, zooplankton still made up a large proportion of the fish diet, showing that this floodplain subsidy extends many miles from its point source. When we looked at the sulfur isotope values of the stomach contents we found that the fish eating at the downstream sites had a strong floodplain signature while the upstream fish had a clear river signature, definitively proving that the downstream fish were eating from subsidy-derived food webs (Bell-Tilcock et al unpublished data).

While upstream fish primarily ate chironomids, fish downstream of the subsidy predominantly ate zooplankton pictured above, especially large cladocerans. Juvenile salmon were measured weekly–here is a particularly plump downstream fish. Photo credit–Bryce Craig at Pusher, Inc.

Most importantly, we found that fish receiving the subsidy grew much faster than the upstream fish. The salmon at the export pump grew in weight an average of 12x faster than the fish not receiving the subsidy, and even the fish six miles downstream grew around 6.5x faster. Managed agricultural subsidies can mimic natural wet year flood patterns and create a food-rich flood pulse during dry years, when juvenile salmon face a barrage of environmental threats and experience high mortality rates. These subsidies can help mitigate the damage of the bad years in the boom-and-bust cycle California Chinook salmon are undergoing, which are projected to become even more severe under climate change.

California Trout is leveraging these data to support their Fish Food on Floodplain Farm Fields project, which is expanding the number of rice farms exporting zooplankton-rich water into the Sacramento River. This project is a a reminder that conservation opportunities exist even in heavily modified working landscapes, but for management strategies in these systems to work they need to bring together diverse stakeholders and find multiple coexisting uses for the same areas of land. By using rice fields to restore a landfloodplainriver trophic subsidy that used to occur widely throughout the Central Valley, we can help juvenile salmon grow big enough to survive their dangerous downstream migration.

Nicholas Wright is junior specialist in the Johnson-Jeffres research group.

Further Reading:

Bell-Tilcock, M.N. et al. (2020) Advancing diet reconstruction in fish eye lenses. Methods in Ecology and Evolution. 12(3), 449-457.

California Trout (2021) Fish food from floodplain farm fields: 2021 Annual report of experimental results. 

Jeffres, C.A (2011) Frolicking fat floodplain fish feeding furiously.

Jeffres, C., Holmes, E. and Rypel, A.L. 2019. Fish are born free, but are everywhere in cages this spring,

Jeffres, C.A., Holmes E.J., Sommer T.R., Katz J.V.E. (2020) Detrital food web contributes to aquatic ecosystem productivity and rapid salmon growth in a managed floodplain. PLoS ONE 15(9): e0216019.

Katz, J.V.E. et al. (2017) Floodplain farm fields provide novel rearing habitat for Chinook Salmon. PLoS ONE 12(6): e0177409.

Mount, J., A.L. Rypel, and C. Jeffres. 2023. Nature’s gift to nature in early winter storms.

Nguyen, Megan. (2017) Yolo Bypass: the inland sea of Sacramento.

Rypel, A.L., D.J. Alcott, P. Buttner, A. Wampler, J. Colby, P. Saffarinia. N. Fangue, and C.A. Jeffres. 2022. Rice and salmon, what a match! 

Sturrock, A.M., Ogaz, M., Neal, K., Corline, N.J., Peek, R.A., Myers, D., Schluep, S., Levinson, M., Johnson, R.C, and Jeffres, C.A. 2022. Floodplain trophic subsidies in a modified river network: managed foodscapes of the future? Landscape Ecology. 37, 2991–3009.

Torres, F., M. Tilcock, A. Chu, and S. Yarnell. Five “F”unctions of the Central Valley floodplain.

Wright, N. 2023. Hidden links between aquatic and terrestrial ecosystems: part 1 – Sierra Nevada lakes.

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A “Peak” into California’s Alpine Lakes and their Food Webs

By Christine A. Parisek

“The Sierra Nevada is five hundred miles of rock put right. Granite freed by glaciers and lifted through clouds where water, frozen and fine, has scraped and washed it into a high country so brilliant it brings light into night.” – Willard Wyman

Alpine lakes are fascinating ecosystems. They are recognized for their clear and pristine appearance, and are mostly cold-water environments nestled into rugged high elevation landscapes. These lakes harbor unique and interesting plant and animal species adapted to thrive in the seemingly harsh environment. The goal of this blog is to introduce California Waterblog readers to California’s alpine lake resources and to highlight the significance of effectively managing these valuable and increasingly vulnerable ecosystems. As a researcher in mountain lake ecology, I’m excited to share some of my field research and provide an overview for why these lakes offer unique opportunities to learn about California’s freshwater resources and food web ecology.


Fig 1. Map of the Cascade-Sierra Province. Source: National Park Service,

California’s Sierra Nevada mountain range spans from northern to southern California and is adjacent to the Cascade mountain range. The Sierra is mostly comprised of granite, supplied with volcanic substrate in the north. Lakes in the Sierra are coldwater systems driven by snowmelt and ice dynamics, and >75% of California’s water comes from the Sierra Nevada-Cascade snowpack. In the north where volcanic rock takes over granite, the lakes are able to receive more groundwater inflow. Sierra Nevada lakes >6,000 feet were historically fishless; however, recreational fisheries programs dating back to the mid-1800s made it commonplace to stock fishes in mountain lakes so that now at least 60% of water bodies contain introduced fishes, especially trout. The introduction of a top consumer into these sensitive cold-water systems has negative and well-known ripple effects on the native biota and the entire food web.

Fieldwork in high mountain lakes 

My ongoing research specifically explores lake food web structure and function across heterogeneous mountain landscapes. For the past four summers I’ve led a field crew to remote mountain lakes in the Sierra Nevada to sample lake food webs as part of the “Sierra Fishes” Project. My team each backpacks ~75lbs into the backcountry to sample as many lake food webs as we can over the summers. We carry a cooler filled with dry ice for sample storage, an inflatable packraft, fish nets and various measuring supplies, a van dorn water sampler, plankton net, aquatic insect survey gear, and of course camping gear and food. We do our best to pack light (spoon toothbrush, anyone?) but field gear just weighs what it weighs! (Fun fact: 30lbs of dry ice only lasts about 4 days in the mountains!) Volumetrically, the study lakes range 20,000 – 48,000,000 m3 and are selected to be at a roughly constant elevation within each basin; thus the sampled systems span 3 orders of magnitude in volume. The lakes harbor a range of fishes, including golden trout, brook trout, rainbow trout, brown bullhead catfish, speckled dace, tui chub, suckers, and shiner; though usually no more than 1-3 fish species will be present per lake. Sampling a whole lake food web means we collect bits of tissue from anything living in the lake – fishes, zooplankton, aquatic insects, algae, plants, diatoms – we put the samples on ice and trek them back to the lab for workup and isotope analysis. By analyzing the isotope data of the tissues, we can reconstruct a comprehensive food web that sheds light on dynamics of the lake’s ecology, functioning, and the roles of organisms within each lake. This information is valuable for effective lake management and future conservation efforts.

Fig 2. Emily Jacinto inflates a packraft at a mountain lake in the Sequoia-Kings Canyon National Park. Photo by Christine Parisek.

Cottonwood Lakes 

Fig 3 (Top). Excerpt from the paper: Curtis, B., 1934. The golden trout of Cottonwood Lakes (Salmo agua-bonita Jordan). Transactions of the American Fisheries Society, 64(1), pp.259-265.
Fig 4 (Bottom). Three California golden trout exhibiting different spot patterns. Photo by Christine Parisek.

One of my favorite regions in the Sierra Nevada is the Cottonwood Lakes Basin. Backpackers in this area will often be acclimatizing to high elevation prior to scaling Mt. Whitney (14,505 ft), the tallest peak in the contiguous United States. You’ll likely also run into the organizers of the Golden Trout Wilderness School at Golden Trout Camp, who shared with our crew aspects of the forest most people miss on the famed hike. The Cottonwood Lakes are at high elevation (~11,000 ft), represent a collection of moraine lakes, and are home to several populations of introduced and isolated California golden trout (Oncorhynchus mykiss aguabonita). Golden trout, the California state fish, are native to just two streams in Southern California (Golden Trout Creek and the South Fork Kern River). Golden trout’s arrival into the Cottonwood Lakes was, as Curtis (1934) describes, “in 1876… thirteen fish were carried by ranchers in a tea-pot across the divide into Cottonwood Creek… in 1891 a further transplant was made… to the lakes…”. Currently, golden trout are maintained at the lakes and managed by the California Department of Fish and Wildlife as a source of eggs for the Mt. Whitney Hatchery. … And, they are notoriously difficult to catch on a fly! (Fig. 5: a cold Mackenzie in the wilderness, without a fish, shrugging).

Fig 5. A cold Mackenzie Miner in the wilderness, without a fish, shrugging. Photo by Colby Hause.

Managing mountain lakes

Mountain lakes in California span the entire state, they hold vulnerable and endemic species, and contribute substantially to recreational fisheries, yet they do not receive the same attention or funding as other local systems. 

Understanding mechanisms that drive lake ecosystems in the mountains is a tricky business. You might think all mountain lakes are the same, so why bother trying to reach so many? Well, they are not! Large vs small lakes, high elevation vs lower montane lakes, and even northern California vs southern California lakes are just a few contributing factors that can truly drive the ecology and ecosystem dynamics of waterbodies. The lakes are highly sensitive to climate change, snowmelt dynamics, and wildfire activity, and are therefore indicators of the health of the surrounding landscape overall.

At the regional scale, we face many questions such as – What is happening to these fragile systems over time? How will the ecology of lakes respond to climate change? How can we better understand lake stressors and habitat fragmentation or loss? What role does wildfire play in this dynamic? Which lakes should be managed for fisheries, and which not?

Owing to the difficulty in accessing these sites, the numerous waterbodies, and the short lake ice-off window providing the opportunity to do so (approximately June – September), high elevation aquatic habitats are generally just poorly studied systems. The Sierra Nevada, with >12K waterbodies, is no exception. Conducing any fieldwork also encompasses major tradeoff – you must choose to either cover a lot of ground with a light sampling regime or perform extensive sampling but ultimately reach fewer total locations. Ultimately these two styles will address different types of research questions. 

Alpine lakes in California are a beautiful and underappreciated natural resource. One of the goals of my work is to raise awareness about the importance of lakes to the ecology of California more broadly. Additionally, lakes can be useful for testing ecological principles of broader relevance (Carpenter et al. 1985; Scheffer et al. 2001; Shurin et al. 2002; Carpenter et al. 2011). I hope to provide more blogs on my work with these lakes in the future!

Christine Parisek is a Ph.D. candidate in the Graduate Group in Ecology at UC Davis and a science communications fellow at the Center for Watershed Sciences.

Fig 6. A stormy afternoon in the Tahoe National Forest. Photo by Christine Parisek.

Further Reading

Carpenter, S.R., Cole, J.J., Pace, M.L., Batt, R., Brock, W.A., Cline, T., Coloso, J., Hodgson, J.R., Kitchell, J.F., Seekell, D.A. and Smith, L., Weidel B. 2011. Early warnings of regime shifts: a whole-ecosystem experiment. Science, 332(6033), pp.1079-1082.

Carpenter, S.R., Kitchell, J.F. and Hodgson, J.R., 1985. Cascading trophic interactions and lake productivity. BioScience, 35(10), pp.634-639.

Curtis, B., 1934. The golden trout of Cottonwood Lakes (Salmo agua-bonita Jordan). Transactions of the American Fisheries Society, 64(1), pp.259-265.

Eby, L.A., Roach, W.J., Crowder, L.B. and Stanford, J.A., 2006. Effects of stocking-up freshwater food webs. Trends in ecology & evolution, 21(10), pp.576-584.

Knapp, R.A., 1996. Non-native trout in natural lakes of the Sierra Nevada: an analysis of their distribution and impacts on native aquatic biota. In Sierra Nevada ecosystem project: final report to Congress (Vol. 3, pp. 363-407). University of California, Davis: Centers for Water and Wildland Resources.

Kraemer, B.M., Pilla, R.M., Woolway, R.I., Anneville, O., Ban, S., Colom-Montero, W., Devlin, S.P., Dokulil, M.T., Gaiser, E.E., Hambright, K.D. and Hessen, D.O., Higgins S.N., Jöhnk K.D., Keller W., Knoll L.B., Leavitt P.R., Lepori F., Luger M.S., Maberly S.C., Müller-Navarra D.C., Paterson A.M., Pierson D.C., Richardson D.C., Rogora M., Rusak J.A., Sadro S., Salmaso N., Schmid M., Silow E.A., Sommaruga R., Stelzer J.A.A., Straile D., Thiery W., Timofeyev M.A., Verburg P., Weyhenmeyer, G.A., Adrian, R. 2021. Climate change drives widespread shifts in lake thermal habitat. Nature Climate Change, 11(6), pp.521-529.

Moser, K.A., Baron, J.S., Brahney, J., Oleksy, I.A., Saros, J.E., Hundey, E.J., Sadro, S., Kopáček, J., Sommaruga, R., Kainz, M.J. and Strecker, A.L., Chandra S., Walters D.M., Preston D.L., Michelutti N., Lepori F., Spaulding S.A., Christianson K.R., Melack J.M., Smol J.P. 2019. Mountain lakes: Eyes on global environmental change. Global and Planetary Change, 178, pp.77-95.

Parisek, C.A., Marchetti, M.P. and Cover, M.R., 2023. Morphological plasticity in a caddisfly that co-occurs in lakes and streams. Freshwater Science, 42(2), pp.161-175. 

Scheffer, M., Carpenter, S., Foley, J.A., Folke, C. and Walker, B., 2001. Catastrophic shifts in ecosystems. Nature, 413(6856), pp.591-596.

Schmeller, D.S., Urbach, D., Bates, K., Catalan, J., Cogălniceanu, D., Fisher, M.C., Friesen, J., Füreder, L., Gaube, V., Haver, M. and Jacobsen, D., Roux G.L., Lin Y., Loyau A., Machate O., Mayer A., Palomo I., Plutzar C., Sentenac H., Sommaruga R., Tiberti R., Ripple W.J. 2022. Scientists’ warning of threats to mountains. Science of the Total Environment, 853, p.158611.

Shurin, J.B., Borer, E.T., Seabloom, E.W., Anderson, K., Blanchette, C.A., Broitman, B., Cooper, S.D. and Halpern, B.S., 2002. A cross‐ecosystem comparison of the strength of trophic cascades. Ecology Letters, 5(6), pp.785-791.

Smits, A.P., MacIntyre, S. and Sadro, S., 2020. Snowpack determines relative importance of climate factors driving summer lake warming. Limnology and Oceanography Letters, 5(3), pp.271-279.

General Interest

Video: How fish are stocked in high elevation lakes, Youtube,

Video: Zooplankton sampling in an alpine lake for the “Sierra Fishes” Project, Christine Parisek,

Video: “Stream Macroinvertebrates, A Love Story” by Kyle Phillips, Center for Watershed Sciences Youtube Channel,

Natural History of the Sierra Nevada, California Naturalist Series 2015,

Water Supply in the Sierra Nevada, Sierra Nevada Conservancy,

Cottonwood Lakes Trail, Forest Service,

Scaling Mt. Whitney,,

Golden Trout Wilderness School Summer Programs,

California Golden Trout, California Department of Fish and Wildlife,

California Golden Trout, California Trout,

NSF RAPID: Food webs of 10 lakes before and after a mega-wildfire,

SOS II: Fish in Hot Water, California Trout,

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Living with Extreme Floods in California

by Peter Moyle, Jay Lund, Andrew L. Rypel, Carson Jeffres and Nicholas Pinter

A close call: View of Oroville Dam’s main spillway (center) and emergency spillway (top), on Feb. 11, 2017. The large gully to the right of the main spillway was caused by water flowing through its damaged concrete surface. (William Croyle/California Department of Water Resources)

Floods and their consequences are a reality for many worldwide, including those living in California. This reality is evidenced by pictures of people stranded on roofs surrounded by water, people paddling down water-filled streets in makeshift boats, and farm fields and orchards covered in standing water. However, there is also growing acceptance that floods are natural, recurring events that have positive aspects, especially where they support migratory waterfowl, enhance fisheries, and sustain wetlands and their high diversity of organisms (Mount et al 2023). In fact, most communities on large rivers globally rely on annual flooding for soil nutrient replenishment, transportation, and maintenance of larger ecosystems that supply food resources (e.g., Amazon, Nile, Okavango, Ganges, Mekong rivers). In California much of our most productive farmland is actually former floodplain, including the once vast wetlands of the Central Valley and the bed of Lake Tulare (Moyle 2023). Most of our cities also are partially built on former floodplains. It is no wonder then that levee building, from the beginning, has been a major activity in the state (Kelley 1989). But the water keeps challenging our defenses, a situation worsening with climate change. This creates major hardships for people and the remaining native biota of California, especially fishes. It is no coincidence that many threatened native species depend on floodplains and their connected wetland and riparian systems. Yet decades of research projects at the UC Davis’ Center for Watershed Sciences on floodplain ecology in California shows that floodplain habitat restoration can benefit fish and wildlife while concurrently reducing flood impacts on the built environment (Opperman et al. 2017).  

Understanding large floods and applying that understanding to flood management is important if we are going to live with floods, rather than always fighting them (Lund et al. 2023; Lund 2012). The traditional idea that all floods can be controlled is naïve and wrong, but remains popular and politically expedient. Repeated onslaughts of “atmospheric rivers” remind us of the vulnerability northern California to flooding, even while we rejoice at the great increase in water stored behind dams and in the mountain snowpack, as occurred this year. But what if the storms had been even bigger and more frequent, as happened in 1861-62 when the Central Valley became an inland sea (Kelley 1989)? Is existing infrastructure up to the task for ‘controlling’ such truly large floods?  

Developing alternatives to traditional flood management is urgent as global warming increases the frequency and size of flooding events in waters from small creeks to big rivers and adds floods considerably larger than those previously experienced. The geologic and historic records show such extreme floods (often called megafloods) will occur and global warming makes it likely they will occur more often (Ingram and Malamud-Roam 2013; Huang and Swain 2022).  

Opperman et al. (2017) presents a positive view of floods and flooding, through a review of the ecology and management of floodplains in temperate regions. They present several maxims[1]to form the basis for a floodplain management strategy that recognizes how floods benefit both people and nature, as well as being harmful. Here we present a revised list of eleven such maxims that provide some foundational truths about floods, flooding, and floodplains in California, especially in relation to fish and wildlife populations. The maxims also need to be viewed in the context of the California water model (described by Pinter et al. 2019) which describes how the success in solving California water issues depends on “far-sighted incrementalism” and learning from failures. These maxims are good companions for further application of the California model.  

1. A bigger flood is always possible. Both recent and geologic evidence support this statement. For example, the Eel and Klamath rivers experienced record flooding in 1955, which produced some huge flows. An even bigger flood occurred in 1964 when the Eel River flood crested at 46 ft (14 m) above ‘normal’ (  Records of sediment deposition in the Central Valley indicate such extreme floods have a recurrence interval of about 100-200 years (Ingram and Malamud-Roam (2013). However, as the Eel River example shows, nature does not care about average return intervals, especially with a changing baseline due to climate change. Native fishes have adaptations to survive and even thrive in big floods. Species such as Sacramento splittail and Chinook salmon have life histories that can take advantage of extended flooding for rearing of their young. But extreme floods remain a big unknown in terms of their potential effects on fish and wildlife in today’s highly altered landscape.  

2. The current water management infrastructure is aging and increasingly likely to fail without major investments in repair, rehabilitation, and/or reinforcement. Effects of dam and levee failures on fish and wildlife can only be guessed at, but will depend on when and where failures occur. Dam failures are not new to California, but the recent failure of Oroville Dam spillways is a recent reminder that this can happen, especially given that California dams median age is 75 years. When dams, levees, and other types of flood infrastructure are overwhelmed by extreme flows, failure can have catastrophic consequences (Cox 2023), especially if a dam failure causes a domino effect of failures downstream. Cox (2023) notes that some dams can fail not only from deterioration but from not being designed to handle extreme events. Leaving impacts on people aside, what happens to the fish and wildlife populations with dam failures and more extreme floods? California’s inland fishes persisted through extreme floods in the past (Moyle 2002). So fish populations should continue to persist if enough individuals survive over a wide area. This means present-day conservation efforts for our declining endemic fishes must succeed before the next extreme flood arrives.  

3. Flood flows shape the landscape. The bigger the flood flows, the more they will bring changes to habitats for fish and people. In California, people generally have a low appreciation for how the landscape was shaped by big floods, from the erosion of canyons in the mountains to the deposition of sediment on the valley floor, estuaries, and coasts. The floor of the Central Valley reminds us that extreme floods tend to even out this landscape, creating a flat topography interlaced with drainage systems, sloughs, and streams. This topography allowed construction of the fields that support productive farms and floodable habitats for fish and wildlife. Extreme flows should thus be expected to alter the landscape, eroding sediment here, depositing sediment there, carrying some into estuaries. If there is insufficient room for this action in existing floodplains and bypasses, big flows will create room by washing away levees, eroding farmland, enlarging sloughs, recreating drainageways and other processes. When “record” flood flows come again, providing Room for the River ( see#5) will be regarded as genius. The native fishes will appreciate it as well. The question becomes: Will our society have the wisdom, creativity, and resources to make room for extreme floods, even greater than the legendary 1861-62 flood of the Central Valley and southern California or the 1964 flood of the Eel, Klamath, and other coastal rivers?  

4. Years between floods are the best times to reassess floodplain management. Calls to reduce the damaging effects of floods peak as flood waters recede but solving flood problems can be quickly neglected as other crises develop. The dry intervals between floods, especially if long and droughty, tend to reduce attention and investments for living with floods, including extreme floods. Non-flood years have traditionally been times to repair or expand levees and dams. But dry years also should be the time to carefully designate floodable lands and to build ecologically-friendly flood infrastructure, especially bypasses around cities. Developing ‘green’ infrastructure that allows us to better live with floods, rather than fighting them, will be a long and costly, but can pay off with reduced damage in urban areas, loss of species and habitat, and loss of human life. It can also pay off in terms of increased abundance of fish and wildlife, perhaps even reversing the declines of some species, and improved recreation and quality of human life in flood and non-flood years.                         

Yolo Bypass in flood. The flooded fields can support large numbers of migratory waterfowl and fish. Photo by Carson Jeffres.  

5.  The best protection against a damaging flood is a large, well-managed floodway that keeps floods away from people and keeps people away from floods while providing habitat for native fish and wildlife. Levees and dams tend to give a false sense of security about being immune to flooding. Incidents like the Oroville Dam spillway failures in 2017 or repeated, if infrequent, returns of Lake Tulare can ‘shake up’ people but are quickly forgotten ( People like to build on cheap, flat floodplain land and expect to be protected from floods. But at some point, our society will recognize that it is less costly to purchase houses and other structures on floodable land, than to keep building bigger levees, paying for disaster assistance, and suffering flood damages (Schaefer and Sanders 2020). The Yolo Bypass is a good example of a well-managed floodway; it routes flood water away from the city of Sacramento while providing habitat for fish and wildlife. In most years, it also supports productive agriculture. The bypass is now being enlarged to accommodate larger floods and additional benefits. The future lies with creating more green infrastructure, such as designated floodplains that support wetlands and riparian forests. Levee setbacks can be part of the green infrastructure approach. This is referred to as making ‘Room for the River’ in the European literature. Increasingly floodable agricultural land is being valued in this regard as well, partly because such lands can also contribute to groundwater recharge. Traditional ‘gray infrastructure”, such as dams and levees ultimately have to be replaced or repaired at great expense. In California significant parts of this infrastructure may be past due for replacement (Cox 2023).  

6. Flood management is most effective when implemented at the scale of the entire river basin or watershed. Much damage from the great floods on the Eel and other north coast rivers in 1955 and 1964 was from poorly regulated logging that destabilized geologically fragile slopes and sent huge amounts of sediment and debris down the river, destroying towns and natural habitats. Yet the massive redwood and fir trees that historically stabilized the watershed and were the object of logging, were growing most luxuriantly in sediment delivered by decades of previous floods. Forests are currently threatened by increased fire severity from a century of poor fuel management and a warming climate and although the cause is different, harmful floods are increasingly likely. Recognizing the importance of watersheds in flood management means using on a diverse portfolio of management methods that work with natural processes. Anadromous fishes such as Chinook salmon, coho salmon, and steelhead rainbow trout particularly benefit from this approach because they have life histories that use different parts of the watershed, as well as the ocean, at different times in their life cycle.

Floodplain of the North Fork Eel River, July 2006, showing gravel bars created in large part by the 1964 flood. The forest next to the river includes the Avenue of Giants, old-growth redwoods.   Photo by Jan Kronsell.  

7. Floodplains can support diverse ecosystems and agriculture simultaneously. This is a basic theme of Opperman et al. (2017). Floodplains and flood-generated lakes in California’s Central Valley once supported the most productive and diverse aquatic ecosystems in the state; the ecosystems in turn supported a large population of indigenous peoples who harvested the abundant fish, wildlife, and plants. Research at UC Davis and elsewhere shows that the remnants of this natural system can be restored to some extent (e.g., Cosumnes River), although these remnants become novel ecosystems where the remaining native biota shares the resources with abundant non-native species, where the land and water are highly altered and where the ecosystem is managed by people. ‘Restored’ floodplains, such as those of the Yolo and Sutter Bypasses, can support abundant migratory fish (salmon, splittail) and waterfowl, as well as resident species (e.g., giant garter snake, river otter) in specially managed areas. The two bypasses also support diverse and productive agriculture, which can be compatible with rearing fish and waterfowl. Creating room for large-scale floods does not have to create a disaster for fish, wildlife, and farmers. Large scale floods can have benefits, if respected and understood.  

8. Flood flows are important for the productivity of estuaries and near-shore marine environments. We should stop thinking that floodwaters are “wasted to the sea” (Cloern et al. 2023). They provide nutrients and sediments needed for estuarine and marine ecosystems, likely increasing the production of harvestable species. We tend to forget that flood flows connect land, river, and ocean habitats, and ocean productivity can be returned to inland waters by anadromous fishes such as salmon. Preparation for extreme floods also has benefits for improving protection from more frequent ‘regular’ flooding and providing fish and wildlife habitat as well as recreation for people in most years.  

9. California’s endemic native fishes are adapted for persisting though major floods and droughts (Moyle 2002). However, it is not known if they can persist under the extreme circumstances from extreme floods following a long drought and then interacting with today’s highly altered landscape. The basic strategies of fish for surviving extreme events are (1) hunker down, (2) go with the flow, (3) be someplace else when the floods occur (e.g., at sea or in lakes), and (4) be lucky to survive but have a life history that allows for rapid re-colonization. Recognizing these strategies could allow for creation or protection of survival habitat (e.g., floodplain lakes on edges of bypasses) before extreme floods occur.  

10. California’s terminal lakes require flood flows for persistence and rejuvenation. Terminal lakes occur at the bottom of large watersheds that have no further drainage. The water usually enters during high winter/spring flood events and leaves mostly by evaporation, although some lakes connect to rivers in major floods. As a consequence, many terminal lakes are quite alkaline (salty) and some cannot support freshwater vertebrates. California has many such lakes including: Goose Lake (on the Oregon border), Eagle Lake (Lassen County), Honey Lake (Lassen Co.), Mono Lake (Mono Co.), Owens Lake (Inyo Co.), Salton Sea (Imperial Co., mostly), and Tulare Lake (Tulare Co.). These are some of California’s most interesting and productive aquatic ecosystems. They function best with steady annual inflow to maintain minimum levels and periodic big floods for rejuvenation and reduced alkalinity. Each of these lakes is unique in its water chemistry, biota, and annual cycles. If a lake dries up because of diversion of inflowing water, or extended drought, the dry lakebeds can produce dust storms, with toxic alkaline dust, which make it hard for people to live close by. The dust storms can be so extensive at times they affect air quality in distant cities, such as when dust from dry Owens Lake or the Salton Sea reaches the Los Angeles region.  

11. Climate change increases uncertainty on the magnitude, extent, and frequency of floods. These conditions look to be much more extreme than most Californians have experienced so far, with longer droughts switching abruptly to extreme wet conditions, as seen in the past decade (Huang and Swain 2022). Given the accelerating warming with its effects on the global hydrologic cycle, extreme floods are highly likely to be part of our near future.  


Investing in green infrastructure to reduce the impacts of major floods on people and native biota is wise and far-sighted policy. Even if extreme floods remain infrequent (not likely), green infrastructure will create a more positive environment for people (e.g., open space, recreation, groundwater recharge, agriculture) and native biota (e.g., expanded wetlands and riparian forests) during the 99% of the time the land is not flooded. Such investment could also pay off for reducing the impacts of inevitable future dam and levee failures. Key investments of this kind will involve ensuring there are places where water can go during floods of all sizes. These include maximizing the extent of Lake Tulare, allowing Delta islands to flood, keeping flood-friendly farmland as farmland, and creating more bypasses around urban areas.                                        

Rio Dell Bridge collapsing into the Eel River, December 1964. Photo by Greg Rumney, North Coast Journal  

Further reading  

Cloern , J.E., J. Kay, W. Kimmerer, J. Mount, P.B. Moyle, and A. Müeller-Solger. 2023. Water wasted to the Sea?, CaliforniaWaterBlog, -sea-2/

Cox, C. 2023. The Trillion Gallon Question: California’s dams are vulnerable; and thousands of lives hang in the balance. How long does the state have to avert disaster? The New York Times Magazine, June 25, 2023.

Dettinger, M.D. and Ingram, B.L., 2013. The coming megafloods. Scientific American308(1), pp.64-71.

Huang, X. and Swain, D.L., 2022. Climate change is increasing the risk of a California megaflood. Science Advances8(31), p.eabq0995.

Ingram, L. and F. Malamud-Roam 2013. The West without Water: What Past Floods, Droughts, and Other Climatic Clues Tell Us about Tomorrow. Berkeley: University of California Press.

Kelley, R.  1989 Battling the Inland Sea. Berkeley: University of California Press.

Lund, J. 2023. Tulare Basin and lake 2023 and their future. California WaterBlog.

Lund, J.R., “Flood Management in California,” Water, Vol. 4, pp. 157-169; doi:10.3390/w4010157, 2012.

Lund, J., D. Des Jardins, and K. Schaefer. 2023. Whiplash again- learning from wet (and dry) years. California WaterBlog

Mount, J., A.L. Rypel, and C. Jeffres. 2023. Nature’s gift to nature in early winter storms.

Moyle, P.B. 2002. Inland Fishes of California, Revised and Expanded. Berkeley, University of California Press.

Moyle, P.B. 2023. Lake Tulare and its fishes shall rise again. California WaterBlog.

Opperman, J.J, P.B. Moyle, E.W. Larsen, J.L. Florsheim, and A.D. Manfree. 2017. Floodplains: Processes, Ecosystems, and Services in Temperate Regions. Berkeley: University of California Press.

Pinter, N., J. Lund, and P. B. Moyle. 2019. The California water model: resilience through failure. Hydrological Processes 2019: 1–5.

Rypel, A.L. et al. 2023. What’s the problem with deadbeat dams?

Schaefer, K. and B. F. Sanders, 2020. Can we talk? California WaterBlog,    

The authors of this blog are all affiliated with the Center for Watershed Sciences at the University of California – Davis.  

[1] A maxim is “a short pithy statement expressing a general truth or rule of conduct” – Google

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