United States 

Environmental Protection Agency 

Office of Water 

4305T 

EPA-823-F-09-008

September 2009

EPA Releases Report on 

Fish Contamination in U.S. Lakes 

and Reservoirs 

EPA is releasing the final report for the National Study of Chemical Residues in Lake Fish 

Tissue, a statistically-based national survey of contaminants in fish from lakes and reservoirs in 

the lower 48 states. For four years, EPA worked with 47 states, three tribes, and two other 

federal agencies to collect fish from 500 lakes and reservoirs selected randomly from the 

estimated 147,000 target population of lakes and reservoirs in the 48 states. Analysis of fish 

samples included 268 persistent, bioaccumulative, and toxic (PBT) chemicals, most notably 

mercury, polychlorinated biphenyls (PCBs), and dioxins and furans. Results show that mercury 

and PCBs were detected in every fish sample from all 500 lakes and reservoirs. Mercury 

concentrations in fish fillet samples exceeded EPA’s recommended tissue-based water quality 

criterion of 0.3 ppm at 49% of the sampled population of 76,559 lakes. 

Background

EPA completed the largest national freshwater fish contamination survey conducted to date in 

the United States, the National Study of Chemical Residues in Lake Fish Tissue (or National 

Lake Fish Tissue Study). Two features make this study unique. It is the first national freshwater 

fish contamination survey to have sampling sites selected according to a statistical design, and it 

includes the largest set of chemicals ever studied in lake fish. The statistical survey design 

allowed EPA to estimate the percentage of lakes and reservoirs in the lower 48 states with fish 

tissue concentrations above levels of potential concern for human or ecosystem health. The 

study also provided the first nationally representative estimates of median concentrations of 268 

PBT chemicals in lake fish and defined a national baseline for tracking reductions of these 

chemicals in freshwater fish as a result of pollution control activities. 

EPA worked with 47 states, three tribes, the National Park Service, and Tennessee Valley 

Authority for four years (2000-2003) to 

collect fish from 500 lakes and 

reservoirs selected randomly from the 

estimated 147,000 target population of 

lakes and reservoirs in the lower 48 

states. The lakes and reservoirs sampled 

for the study ranged in size from 2.5 to 

over 900,000 surface acres. Teams of 

biologists used consistent methods 

nationwide to collect samples of a 

predator fish species (e.g., bass or trout) 

and a bottom-dwelling species (e.g., 

catfish or carp) from each lake or 

reservoir. EPA analyzed fillets from the National Lake Fish Tissue Study Sampling Locations (500 lakes) 

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predator samples and whole bodies for the bottom-dweller samples. Target chemicals for this 

study included mercury, 5 forms of inorganic and organic arsenic, all 209 PCB congeners 

(analysis of these individual PCB compounds produces 159 tissue concentration measurements), 

17 dioxins and furans, 46 pesticides, and 40 other semivolatile organic chemicals. 

Results

Results from the National Lake Fish Tissue Study show that mercury and PCBs are widely 

distributed in U.S. lakes and reservoirs. Mercury and PCBs were detected in all of the fish 

samples collected from the 500 lakes and reservoirs selected for the study. Dioxins and furans 

were also frequently detected in the fish samples, but they were not as prevalent in lake fish as 

mercury or PCBs. 

The statistical design of the study allowed EPA for the first time to estimate the percentage of 

lakes and reservoirs in the lower 48 states with fish tissue concentrations above human health 

screening values. These estimates relate to a sampled population of 76,559 lakes for fillet 

concentrations from predator (or game fish) samples collected and analyzed for the study. To 

develop these estimates, EPA used human health screening values of 0.3 ppm for mercury, 0.12 

ppb for total PCBs, and 0.15 ppt (toxic equivalency or TEQ) for total dioxins and furans. Results 

for the three most commonly detected chemicals indicate that: 

• 49% of the sampled population of lakes had mercury tissue concentrations that 

exceeded the 0.3 ppm screening value for mercury, which represents over 36,000 

lakes. 

• 17% of the sampled population of lakes had PCB tissue concentrations that exceeded 

the 0.12 ppb screening value for total PCBs, which represents about 13,000 lakes. 

• 8% of the sampled population of lakes had dioxin and furan tissue concentrations that 

exceeded the 0.15 ppt screening value for total dioxins and furans, which represents 

about 6,000 lakes. 

Data Requests

Due to the size of the data files, EPA released data from the National Lake Fish Tissue Study on 

a set of CDs. These CDs contain quality-assured raw data for all four years of the study in Excel 

files, a data dictionary to aid in interpreting the data files, and the final analytical data quality 

assurance report. The data CDs are available at no charge. To order the CDs, contact Leanne 

Stahl online at stahl.leanne@epa.gov and provide your name, mailing address, and phone 

number. 

For More Information

For more information on the National Lake Fish Tissue Study, please contact Leanne Stahl, 

EPA’s National Lake Fish Tissue Study Manager, by e-mail at stahl.leanne@epa.gov or by 

phone at 202-566-0404. Additional information about the fish study is available online at 

www.epa.gov/waterscience/fishstudy/.