Drought, Fish, and Water in California


Pit River in Modoc County, August 21, 2014.  Drying pools contained mainly non-native fishes.

by Peter Moyle

With a big collective sigh of relief, Californians rejoiced that we have largely recovered from 2012-2016 drought[1].  Streams are flowing.  Reservoirs are full. Crops are watered. Native fishes are reproducing   But this not a time for complacency; if the 2012-2016 drought, the hottest and driest on record, had lasted another year or longer, California ‘s farms, cities, and ecosystems would have been in a dire state, with water in short supply everywhere (Mount et al., 2017, 2018).  This should thus be a time to develop new and better strategies for reducing impacts of severe drought on both natural and developed systems, following the California Water Model (Pinter et al. 2019) of “resilience through failure.”  California has a history of learning from past failures of water management, especially floods, and of avoiding repeating mistakes as a consequence.

Drought, of course, is not confined to California, but is a global problem, which is increasing as the planet warms.  Fish and other aquatic organisms bear the brunt of drought because severe competition with people for water destroys their habitats.  Worldwide, they are facing extinction at increasing rates. This is one lesson from a review of drought effects on freshwater fishes from Canada, California, and Australia (Lennox et al. 2019).  This review shows how fish responded to drought in natural and highly altered waterways worldwide to gain insights into how to keep native fish from going extinct as droughts become more severe. California’s fishes provide especially good insights because most are highly adapted for persisting through long natural droughts; however, many are now threatened with extinction because of actions that exacerbate drought impacts.

To make our review more accessible, we condensed our findings into a list of maxims or aphorisms.  These maxims contain general truths to help managers deal with the enormity of fish conservation problems in an increasingly drought-stricken world. Here are the maxims, somewhat modified from Lennox et al. (2019).

  1. Future droughts will be longer, more frequent, and more severe, creating more stressful conditions for freshwater fishes.
  2. Climate change and human alteration of aquatic ecosystems combine to increase the negative effects of drought.
  3. Fishes survive natural droughts in their native waters through physiological and behavioral adaptations, but all have limits.
  4. Different species respond to drought in different ways, so post-drought fish assemblages are hard to predict, especially in highly altered habitats.
  5.  When natural environmental variability is suppressed by human activity, aquatic ecosystems become homogenized, dominated by a few drought-tolerant fish species, often non-native.
  6. Fish survive droughts by dispersal or migration to other habitats or by finding refuges in remnant habitats where conditions are physiologically suitable.
  7.  The most abundant stream fishes in regions with frequent natural droughts are those with the ability to rapidly disperse and recolonize as both adults and juveniles.
  8. The best drought refuges are usually large rivers, lakes, spring-fed streams, and deep permanent stream pools with ground water inflow.
  9. The bigger and more diverse structurally the drought refuge, the more fishes it can shelter.
  10. Connectivity among habitats is essential for recovery of fish faunas in streams and lakes stricken by drought.
  11. Ground water is essential for maintaining stream refuges through drought.
  12.  Human activity often produces perpetual drought conditions in streams through surface and groundwater removal.
  13. Poor water quality, especially low dissolved oxygen and high temperatures, followed by predation, are primary causes of fish mortality in drought refuges.
  14. Changes in severity or frequency of drought alter fish assemblages, with the effects of the changes depending on the history and physical characteristics of the system.
  15. Fisheries will decrease if human-mediated drought results in habitats unable to support large populations of harvestable fish.
  16. Translocation of species to new waters and artificial propagation are desperation measures unlikely to ameliorate the ecosystem effects of human-expanded drought.

These maxims point to the need to have some aquatic ecosystems in California that are managed largely for native fishes, in ways that make them drought-resistant.  California’s native fishes are actually adapted for surviving severe droughts, but they evolved in large, inter-connected river systems where there were always refuges somewhere.  We cannot bring back those large river systems as habitat but we can create refuges that are closely monitored and managed, with native fishes and the aquatic ecosystems they represent, getting a fair share of the water (Mount et al. 2017).


Oristimba Creek, Merced County, during 2012-16 drought.  Most of creek was dry but there were a few native fish refuges where groundwater  seeped into bedrock pools.  Unfortunately, the pools contained non-native green sunfish which were consuming the native fishes. Photos by P. Moyle.

Further Readings

Lennox R.J., D.A. Crook, P. B.  Moyle, D. P. Struthers, and S. J. Cooke 2019. Toward a better understanding of freshwater fish responses to an increasingly drought-stricken world. Reviews in Fish Biology and Fisheries 29:71-92  https://doi.org/10.1007/s11160-018-09545-9.\  Open Access.

Mount, J., B. Gray, C. Chappelle, G. Gartrell, T. Grantham, P. Moyle, N. Seavey, L. Szeptycki, and B.Thompson. 2017. Managing California’s Freshwater Ecosystems: Lessons from the 2012-16 Drought. Public Policy Institute of California 52 pp.

Mount, J. B. Gray, and 28 others. 2018.  Managing Drought in a Changing Climate: Four Essential  Reforms. San Francisco: Public Policy Institute of California. 30 pp.

Pinter, N., J. Lund, and P. Moyle. 2019.  The California water model: resilience through failure. Hydrological Processes 2019: 1–5. https://doi.org/10.1002/hyp.13447





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

About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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3 Responses to Drought, Fish, and Water in California

  1. Frances Griffin says:

    Will somebody please take seriously the role smart introcuction of beavers can play in restoring the water table and mitigating water flows. We cannot let any resource especially low cost ones go un-used.
    There is abundant research and models to follow, even to the point of min-made beaver dam anlalogs. Utah is ahead of us. So is Washington state. Why are we so slow to learn?

  2. Felice Pace says:

    Yes, natural drought is a threat to fisheries but not so great a threat as the administrative droughts imposed on California streams that have agricultural diversions each and every year. We continue to progressively dewater our streams, most recently via unregulated groundwater withdrawal but also via inadequate regulation where there are adjudicated flow rights.

    I do not accept that we can only get a few fish refugia. We can and should recover all our river and stream systems. All our streams need flow criteria that define the minimum flows fish and stream ecosystems need each month of the year in order to survive and be healthy and that are adopted as legal flow objectives that cannot be violated. But so far the State Water Board is not even willing to enforce adjudicated flow rights. For example, SWRCB allows irrigators to dewater the Scott River every year in violation of the Forest Service right to adjudicated flows in Scott River. That has got to change.

    We will not stop the dewatering and the destruction of fisheries until the SWRCB musters the will to develop, adopt and stand by adequate flow requirements for all California streams. That will take roughly 40% of each streams unregulated, natural flow; currently ag takes 70% or more of all flow. That’s why Peter M is arguing for a few refugia. But I say we can muster the will to restore all streamflows. Humans can learn to live with less…that is, if we want living streams and not dewatered rivers of sand.

  3. George H. Cinquini says:

    We need to not remove dams like Scott Dam (Lake Pillsbury) and manage the water release to protect the salmonids in the Eel River. We need more water storage, not less.
    Better management, and habitat restoration

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