Mercury is top contaminant of CA fish, concludes 2-year SWAMP study

This month, the State Water Resources Control Board released the final report for its two-year study of contaminants in sport fish from CA lakes and reservoirs.  Mercury was found to be the top contaminant of CA fish, followed by PCBs.  The SWRCB’s press release follows.  Click here for links to the report, fact sheet, and frequently asked questions. 


State Water Resources Control Board

June 03, 2010

Contact: Dave Clegern
Office of Public Information, State Water Resources Control Board

Largest-Ever Survey Documents Extent of Contamination in Sport Fish in California Lakes

Sacramento – The State Water Resources Control Board’s Surface Water Ambient
Monitoring Program (SWAMP) has released findings from California’s largest ever
survey of contaminants in sport fish from lakes and reservoirs. The survey found
mercury and polychlorinated biphenyls (PCBs) are the two greatest concerns.

This report represents the end of a two-year survey and presents new data on 122
lakes sampled in 2008, adding to the database covering 150 lakes sampled in 2007
and reported last year. The survey focuses on sport fish because they provide
information on human exposure and also represent the top of the aquatic food chain.

Mercury accumulation in fish is a persistent problem throughout much of the state.

Twenty-one percent of the lakes surveyed had at least one fish species with an
average mercury level that exceeded the Office of Environmental Health Hazard
Assessment (OEHHA) threshold for considering a recommendation of no consumption
for women of childbearing age and children. Methylmercury can affect the developing
nervous system in children and adolescents, potentially leading to learning disabilities.

Mercury contamination of California water bodies is largely a legacy of historic
mercury and gold mining, but can also reach lakes from regional and global emissions
to the atmosphere. However, the degree of mercury contamination in the state’s lakes
is comparable to the average condition observed across the U.S. in a recent national
lakes survey.

PCBs were second to methylmercury as a potential health concern to consumers of
fish caught from California lakes. However, only 1% of the lakes sampled had a
species with an average concentration that exceeded OEHHA’s threshold or
considering a recommendation of no consumption. PCBs may cause cancer, damage
the liver, digestive tract, and nerves; and affect development, reproduction, and the
immune system. PCBs are persistent chemicals that are now banned, but were
commonly used in electrical, industrial and other applications. Other pollutants,
including dieldrin, DDT, chlordanes, and selenium, were also found, but generally at
low levels.

The Lakes Survey focused on nearly 300 of the most popular fishing lakes in the state.

Random sampling of an additional 50 of California’s other 9,000 lakes was included to
provide the basis for a statistical statewide assessment. This initial screening study
was the first step in an effort to identify and quantify contaminants in California’s lakes
to provide a detailed evaluation of human and wildlife exposure. The Lakes Survey was
paid for by funds supplied by the United States Environmental Protection Agency
(USEPA) and monitoring fees paid to the State Water Board for waste discharge
permits. OEHHA will not be able to develop new consumption recommendations based
solely on data from this screening study – more thorough sampling will be required.

The Lakes Survey was the first component of a new program that is tracking sport fish
contamination in all California water bodies. Results from the first year of a two-year
survey of contaminants in sport fish from California coastal waters will be available in
May 2011.

The public can access results for individual fishing locations included in the Lakes
Survey through the California Water Quality Monitoring Council’s “My Water Quality”
web portal at:

Information on sport fish contamination can be accessed by clicking on “Is It Safe to Eat
Fish and Shellfish from Our Waters?”

The Lakes Study Report is available on the SWAMP website at:

The State Water Resources Control Board’s mission is to preserve, enhance, and
restore the quality of California’s water resources, and ensure their proper allocation
and efficient use for the benefit of present and future generations.

Lakes Survey Fact Sheet

How is this survey different from past research on contaminants in California’s
This two-year survey looks at accumulated contaminants at the top of the food chain in
nearly 300 lakes statewide. It is the largest survey of its kind and should provide the
most extensive data ever made available.

What did the survey find?
21-percent of California’s lakes are contaminated with levels of mercury that exceed
thresholds set by the Office of Environmental Health Hazard Assessment (OEHHA) at
or above levels at which OEHHA would recommending no consumption for women of
child bearing age and children.

Will the survey result in such a determination?
No. More sampling is required before OEHHA would make that kind of determination.

Is mercury the only contaminant found at those levels?
No. Polychorinated biphenyls (PCBs) were also found at unhealthy levels in onepercent
of the lakes surveyed.

Who actually performed the survey?
The two-year survey was done by the San Francisco Estuary Institute on behalf of the
State Water Board.

What happens next?
Results of the first year of a two-year survey of sport fish in coastal waters will be
available in 2011.