Delta Stressors

The Sacramento-San Joaquin Delta is an important economic and environmental resource that benefits virtually all of California. The Delta has experienced declines in ecosystem health for many years, but the decline became dramatic several years ago with a sharp decline in populations of delta smelt and several other fish species.

Recently, the Delta Independent Science Board (DISB) prepared a report for the Delta Stewardship Council (DSC) that found no objective method for prioritizing the multiple stressors thought to be responsible for the Delta's decline. The report also found no evidence that suggests reducing just one - or even several stressors - will fix the Delta's ecosystem issues.

Here is a quote from DISB chair, Richard Norgaard, when he presented the Board's report to the Council - as reported by The Stockton Record:

"We're not in a position now - we may be in a position later - to say it's these three stressors that are causing 90 percent of the problem, or one stressor causing 45 percent of the problem… At the present state of knowledge, we just think there's a lot of interacting stressors."

It is clear that the science community is still in pursuit of justified Delta stressors to determine how best to solve the issues in the Delta. The cause(s) of this decline and the appropriate way to mitigate it have been - and continue to be - the subject of much debate among policy makers and interest groups.

Known Delta Stressors

Many stressors have been shown to have a direct impact on Delta. For decades, it has been well-known that water projects which send Delta water to other parts of the state have caused significant negative impacts to Delta fish species.

To inform the planning processes of the Council's Delta Plan and the Bay Delta Conservation Plan (BDCP), the State Water Resources Control Board (State Water Board) developed new flow criteria for the Delta to determine how much water the Delta environment needs to thrive in August 2010. The report determined that reducing the amount of water pumped out of the Delta would improve the Delta ecosystem by protecting threatened fish species like the delta smelt.

The California Department of Fish and Game (DF&G) used the State Water Board's report conclusions to identify scientific biological objectives and flow criteria for the Delta species at risk. A key point illustrated in DF&G's executive summary is that "each native Delta fish species is adapted to the habitat conditions characteristic of the ecosystem. As natural flows and the patterns of those flows have been reduced or altered, flow conditions have become more favorable for nonnative species."

Learn more by reading DF&G's report findings.

Non-native species, or invasive species, have received recent attention for their growing threat on the San Francisco Bay-Delta and impact on the natural ecosystem. These species include clams, plants and zooplankton that are perhaps contributing to fish declines in many ways. For example, non-native overbite clams have profoundly altered the food web since the late1980s. Invasive plants, such as the Brazilian waterweed, are now providing cover for predatory fish that eat the smaller pelagic fishes.

Setting the record straight

In recent years some interests have tried to focus attention on Sacramento's wastewater discharge -- specifically the ammonia it contains - as a main driver in the Delta decline, diverting attention from the impact of Delta water exports. SRCSD's position is that there is a significant lack of sound, scientific evidence to make a definitive connection between ammonia and decline of fish species.

In 2009, an independent expert panel convened by CalFED concluded that too many questions about ammonia's impact on the Delta remain unanswered to draw any definitive conclusions. That panel also indicated that flows are likely more significant and recommended that the State conduct a comprehensive study of all suspected Delta stressors to determine their individual significance and how they relate to one another - so that clear priorities can be determined and a well-founded Delta restoration plan developed. Such a plan has yet to be conducted.

Science supports - and SRCSD acknowledges - the need to reduce a portion of the treatment plant's ammonia by about 50% in the future to prevent any possibility of future low oxygen conditions in the Sacramento River. However, SRCSD's new permit adopted by the Central Valley Regional Water Quality Control Board (Central Valley Water Board) in December 2010 calls for full ammonia removal. SRCSD has asked the State Water Resources Board for a review of the this decision because of the lack of clear data and scientific justification for that and other mandates in the permit.

Fact Sheet: Point-by-point summary of the rebuttal to the "Great Delta Toilet Bowl" misinformation campaign >>>

Fact Sheet: "A Review of Delta Fish Population Losses from Pumping Operations in the Sacramento-San Joaquin River Delta" >>>

Facts on Ammonia and SRCSD's operation:

Fact Sheet: Ammonia >>>

Glibert Study Response (No Smoking Gun Fact Sheet) >>>

Fact Sheet: Operations >>>