Stressed Out—Dealing with the Delta’s non-native landscape

Jay R. Lund, Ray B. Krone Professor of Environmental Engineering, University of California – Davis
Peter Moyle, Professor of Fish Biology, University of California – Davis
Jeffrey Mount, Professor of Geology, University of California – Davis
Ellen Hanak, Public Policy Institute of California
William Fleenor, Research Engineer, University of California – Davis

Pre-development Delta channels (left) and Delta channels today (Sources: Chris Enright and William Fleenor)


The Delta’s non-native landscape

Today’s Delta is thoroughly different from the natural environment in which its native species evolved.  Seven hundred and fifty thousand acres of freshwater and brackish tidal marsh are now 540,000 acres of farmland, 61,000 acres of open water, and 75,000 acres of tidal marshland.  Dams and river levees have reduced upstream spawning and rearing habitat for salmon by more than 70%.  Freshwater inflows to the Delta have also decreased, with roughly 34% less annual inflows now entering the Delta and 46% less outflows, and a highly-altered seasonal pattern.  The internal flows of many Delta channels have been completely reversed by export pumping, so upstream is now often downstream – something understandably confusing to fish.

Farms and cities add large quantities of wastewater and contaminants.  Ship channel dredging and Delta levees have increased salinity intrusion.  The Delta’s channels are now largely armored rip-rap, and nothing like the earlier tidal marshland.  Anglers, marine shippers, wildlife agencies and aquarium hobbyists have brought all manner of invasive species of fish, plants, plankton and clams to the Delta, changing most of the major species in the ecosystem (Lund et al. 2010; Moyle and Bennett 2008).  The Delta is now mostly dominated by a wide variety of non-native fish and plants (Feyrer et al. 2003, 2007; Herbold and Moyle 1989; Moyle and Bennett 2008).

If you were a native fish in the Delta, you would be increasingly stressed as you tried to live as a stranger in a strange waterscape.

What are the stresses on native fish in the Delta?

Stressors on the Delta’s native ecosystem can be organized and identified in many ways.  The Delta Independent Science Board identifies 42 stressors and drivers.  Here is a shorter list of causes, organized to illustrate the broad responsibility for the Delta’s problems.

Biological Causes:

  1. Hatchery management (US Fish and Wildlife Service, California Department of Fish and Game)
  2. Invasive species – invertebrates (ballast water from the shipping industry)
  3. Invasive species – fish (anglers, fish agencies)
  4. Invasive species – plants (aquarium owners, others)


  1. Agricultural runoff (farmers: salts, selenium, pesticides)
  2. Legacy mining wastes (miners: debris and mercury)
  3. Urban runoff (cities and counties: pesticides, other chemicals)
  4. Urban wastewater treatment plant discharges (cities and wastewater districts)


  1. Reduced Delta outflow volume (diverters upstream [56% of diversions]), in-Delta [9%], export pumps [35%])
  2. Changed seasonal Delta outflow pattern (upstream storage and all diverters)
  3. Changed flow patterns within the Delta
    1. From pumping, gates and barriers (diverters in the Delta and export pumps)
    2. From ship channel dredging (Ports of Sacramento and Stockton)
    3. From poldering of marshlands (original Delta landowners, 1860s-1930s)
  4. Reduced San Joaquin River inflows (upstream diverters and CVP operations for exports through south Delta pumps)
  5. Changed Sacramento River inflows (upstream diverters and CVP and SWP operations for exports through south Delta pumps)
  6. Reduced and disruptive Eastside stream inflows (Cosumnes, Mokelumne),  (upstream diverters and groundwater pumping)


  1. Reduced access to spawning upstream of dams (dam owners and operators for water supply, flood control, hydropower and recreation)
  2. Reduction of riparian habitat, seasonal wetlands and floodplains (land developers and residents; flood operations)
  3. Reduction of historical tidal marshland and channel margin habitats (original Delta landowners)
  4. Reduced sediment availability (dams, farming, flood control)

Ocean Conditions: Climate change effects on Upwelling, El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), etc.) (all of us)

Fisheries: (inland and oceangoing commercial fishermen and recreational anglers)

Clearly, many people and interests bear significant responsibility for the decline of native fishes in the Delta, even though they have not intended to harm these fish.  Although most of the fish problems are tied, directly or indirectly, to water management, all of these diverse interests will need to participate in solving the problems.

Why look at multiple stressors?

Acknowledging the many broad causes of the Delta’s native ecosystem decline – or stressors – is inconvenient politically, rhetorically and technically.  But this difficult problem cannot be solved without taking such a broad view.  Here are four reasons for serious and pragmatic assessment of the many stressors contributing to the decline of the Delta’s native fish species.

  1. Civilizing the discussion. Efforts by stakeholders to insulate themselves from responsibility, and cast responsibility on others, are not helpful in solving the problem.  Understanding and acknowledging broad responsibility is needed for a more effective discussion and identification of solutions. (This implies reducing flows of denial.)
  2. Understanding our limits. The Delta’s tremendous historical transformations limit what we can do to recreate native ecosystems.  We sorely need to define and understand technically reasonable environmental objectives for the Delta’s future.
  3. Real knowledge for management. Broad and balanced understanding is needed to help identify and orchestrate more effective and cost-effective actions for desirable futures.
  4. Basis for allocating costs and responsibilities. Solving the Delta’s problems will require real resources.  State and federal governments are unlikely to pay enough; all those who have contributed to the problem or benefit from a solution should participate in supporting solutions.

How to move forward?

How can we maintain native species in the Delta, as part of a ‘healthy’ ecosystem, given the clearly complicated challenges in an environment governed by so many interests desiring different outcomes?  Our institutions and professions are not prepared for dispassionate, solution-oriented conversations on the subject.  Stakeholders are understandably driven by fears.  Scientists tend to get lost in the thickets of knowledge and often can see only their part of the thicket.  Managers have difficulty listening, and even more difficulty acting, given that ostracism can result from taking risks.

We hope to make some suggestions and observations in the coming months.  Perhaps these will be useful in provoking useful discussions.

Some tentative conclusions

  1. The decline of the Delta’s native species has many causes.  Most water users in California and land users throughout the Central Valley over the last 150 years bear some responsibility.
  2. Reversing stressful conditions to restore the Delta to some previous condition is essentially impossible, and current policies of unmanaged change are not sustainable.
  3. Management of the Delta’s ecosystem should focus on supporting a mix of desirable species that can be sustained in the Delta, including native species and others that can thrive under similar conditions.  Although various ongoing policy processes support this general goal, this vision has yet to be articulated in practical terms, except in attempts to manage individual species.
  4. The broad range of Delta interest groups will need to participate in and pay for any effective solutions, given likely shortages of federal and state government funds.  Shifting blame is an ineffective path forward towards any solution.
  5. Effective solutions for reviving the Delta ecosystem will be difficult to negotiate without scientific leadership suggesting workable frameworks to a receptive audience of political leaders.
  6. We will not get it right the first time.  Waiting for perfect science will not halt the declines in native fishes.  Imperfect understanding must guide us in the meantime. This means those with management responsibility must be willing to take risks, so we can learn and adapt with time.

Further Reading:

Bennett W, Hanak E, Lund J, Moyle P. 2008. An expert survey on the viability of delta fish populations. Appendix E. In: Lund J et al. Comparing futures for the Sacramento–San Joaquin Delta. San Francisco (CA): Public Policy Institute of California.

DWR (1995), Delta Water Atlas, California Department of Water Resources, Sacramento, CA.

Feyrer F, Nobriga, ML, Sommer,TR. 2007. Multi-decadal trends for three declining fish species: Habitat patterns and mechanisms in the San Francisco Estuary, California, USA. Canadian Journal of Fisheries and Aquatic Sciences 64(4): 723–734.

Feyrer, F. and M.P. Healey (2003), “Fish community structure and environmental correlates in the highly altered southern Sacramento-San Joaquin Delta,” Environmental Biology of Fishes, Volume 66, Number 2, Pages 123-132.

Herbold B, Moyle PB. 1989. Ecology of the Sacramento–San Joaquin Delta: A community profile. U.S. Fish and Wildlife Service Biological Report, Vol. 85. No. 7.22.

Lund, J., E. Hanak, W. Fleenor, W. Bennett, R. Howitt, J. Mount, and P. Moyle, Comparing Futures for the Sacramento-San Joaquin Delta, University of California Press, Berkeley, CA, February 2010.

Moyle PB, Bennett WA. 2008. Future of the Delta ecosystem and its fishes. Appendix D. In: Lund J et al. Comparing futures for the Sacramento–San Joaquin Delta. San Francisco (CA): Public Policy Institute of California.

Thompson J. 1957. Settlement geography of the Sacramento–San Joaquin Delta, California [PhD dissertation]. Stanford University.

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