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Water Resources of Washington State

USGS Fact Sheet FS-102-97
by Martha L. Erwin and Mark D. Munn
August 1997
Are walleye from Lake Roosevelt contaminated with mercury?[TITLE]

To find out, scientists from the U. S. Geological Survey (USGS) tested walleye and other sport fish
from the upper Columbia River and Franklin D. Roosevelt Lake (Lake Roosevelt), the largest reservoir
in Washington and a popular fishing spot.


After reviewing these findings, the Washington State Department of Health concluded that people who regularly consume large amounts of Lake Roosevelt walleye may be at risk of adverse health effects from mercury and should limit their consumption of these fish (see Recommended Maximum Consumption of Walleye from Lake Roosevelt).

[photo of angler with a walleye he caught]

A Spokane Walleye Club member shows
off a walleye from Lake Roosevelt.
Local people caught most of the fish
for this study. (Photo by Dick Lee.)

Why worry about mercury?

Mercury, a metal like lead or tin, comes from many natural sources, such as oceans, volcanoes, and the weathering of rock in mountains. Human activities like burning fossil fuels and discharging industrial waste into the air and water also add mercury to the air we breathe, the water we drink, and the food we eat. We all have mercury in our bodies, but at levels that are typically not high enough to cause health concerns. It is possible, however, to accumulate too much mercury in the body.

The greatest source of mercury for most people is the fish they eat. Most mercury in fish is methylmercury, a highly toxic substance that can build up in predatory fish such as walleye, swordfish, and tuna, and in animals that eat these fish.

Methylmercury can damage the brain, nervous system, and kidneys. The risk is probably very low for adults who eat fish only occasionally. The risk is greatest for developing fetuses, children, and people who depend on sport fish for food.

Mercury also threatens the health of fish-eating wildlife such as loons, eagles, otters, and raccoons. Some evidence suggests that at very high concentrations it harms the fish themselves. And, mercury-contaminated sport fish may adversely affect a local economy that depends on recreational fishing.

It's the amount that counts

Why were fish from Lake Roosevelt tested for mercury?

All waterbodies contain some mercury, but not all sport fish are tested for mercury. People were concerned about fish from Lake Roosevelt because it's a popular fishing area and because

Mercury in the aquatic food chain (GIF, 36457 bytes)[Mercury Cycle image]

Why focus on walleye?

How the study was done

"This study was a cooperative effort--other agencies and the public helped us out from the beginning," said USGS biologist Dr. Mark D. Munn.

Collecting a lot of fish was necessary because testing fish (not the water) is the only way to determine if they're contaminated. Mercury goes through a complex cycle in the environment, and mercury levels in water vary. Because methylmercury bioaccumulates and biomagnifies in tissue, highly contaminated fish may be found in water that is very low in mercury.

In the summer of 1994, USGS scientists and Spokane Walleye Club members collected fish from three areas where fishing is popular and where mature walleye spawn. Most of the walleye caught were about 3 years old and 15 inches long; they also caught smaller numbers of smallmouth bass and rainbow trout, two other popular sport fishes in Lake Roosevelt, so they could be compared to walleye. (See "Composite samples" for more information.)

[Map image] Map of fish collection areas (GIF, 17673 bytes)

How do Lake Roosevelt walleye compare . . .

. . . to sport fish from the rest of the U.S.? Average mercury levels in local fish were generally similar to or less than levels in fish from across the country (see graph). The average concentration of mercury in walleye from Lake Roosevelt was 0.3 parts per million (ppm; equivalent to 0.3 milligrams of mercury in a fish weighing 1 kilogram), less than 0.52 ppm, the national average for walleye in a 1992 study by the U.S. Environmental Protection Agency (USEPA). However, the USEPA fish probably had unusually high levels because most of the fish-collection sites were located near industrial sources of contaminants.

[Graph image] Average mercury concentrations in walleye (GIF, 16666 bytes)

. . . to standards designed to protect human health? Mercury levels in Lake Roosevelt fish did not exceed the limit of 1.0 ppm set by the U. S. Food and Drug Administration (FDA). This limit is intended to protect people who occasionally eat commercially caught fish that come from a variety of fishing areas and contain varying levels of mercury. According to the FDA, the most popular commercial fish (including canned tuna, salmon, and shrimp) usually have less than 0.2 ppm of mercury.

Each state is responsible for advising people about the safety of eating local sport fish. In Washington State, consumption recommendations are established on a case-by-case basis. See below for recommendations about eating walleye from Lake Roosevelt.

What is being done about mercury in fish?

Because it's impractical to test fish everywhere, scientists are working to better understand (1) how mercury changes into methylmercury and (2) how methylmercury bioaccumulates in sport fish. This information will help identify waterbodies and fish that are likely to be contaminated.

According to the results of this study, fishing at a point far away from a known source of mercury doesn't mean the fish are less contaminated than at sites closer to a contamination source (fish from Kettle Falls Reach, closest to the smelter in Canada, had less mercury than fish farther downstream). Anglers and people who eat sport fish should be kept informed.

Although mercury can't be eliminated from lakes or rivers, human activities that add mercury to the environment can be controlled. For example, the Canadian smelter has stopped discharging slag to the Columbia River and has improved its waste treatment methods, thereby reducing its input of mercury and other metals to the river.

A message from the Washington Department of Health

[Image of mother and child]
What's important is how much walleye and other mercury-contaminated fish you eat, not whether you eat walleye from Lake Roosevelt. Because developing fetuses are especially sensitive to the toxic effects of methylmercury, pregnant women and women of childbearing years should watch their diet carefully.

According to the results of the U.S. Geological Survey study, the average amount of mercury in Lake Roosevelt walleye (approximately 0.3 parts per million) does not exceed federally allowed levels. However, these levels were set assuming people eat only a small amount of contaminated fish. If you eat large amounts of walleye frequently, you may be at risk of adverse health effects because the hazard of methylmercury depends on the amount you eat, how often you eat it, and your health. The Washington State Department of Health (DOH) advises you to follow the guidelines below, which are based on an evaluation of methylmercury toxicity by the U.S. Environmental Protection Agency. If you are exposed to mercury from other food sources, such as consumption of other predatory fish like swordfish and tuna, you should eat less walleye than recommended below:

Recommended Maximum Consumption of 
Walleye from Lake Roosevelt
Adults                               Pregnant women and         Children
                                     women in childbearing      under 6
                                     years                      years of age

4 pounds per month                   1 pound per month          1/3 pound
(about 8 meals per                   (about 2 meals per month)  per month

How can I reduce my risk?

Because methylmercury is distributed throughout the tissues of a fish, it cannot be removed by special cooking or trimming methods. Reducing the amount of contaminated fish you eat is the only sure way to reduce exposure to methylmercury in fish. However, eating smaller fish and eating a variety of species will likely help reduce exposure.

For more information, contact the Washington DOH at (888) 586-9427. Visit the DOH home page at

This fact sheet is based on

Munn, M.D., Cox, S.E., and Dean, C.J., 1995, Concentrations of mercury and other trace elements in walleye, smallmouth bass, and rainbow trout in Franklin D. Roosevelt Lake and the upper Columbia River, Washington, 1994: U. S. Geological Survey Open-File Report 95-195, 35 p. (For copies, write or call: Earth Science Information Center, Box 25286, MS517, Denver Federal Center, Denver CO 80225; (303) 202-4210.)

Munn, M.D. and Short, T.M., 1997, Spatial heterogeneity of mercury bioaccumulation by walleye in Lake Roosevelt and the upper Columbia River, Washington: Transactions of the American Fisheries Society, v. 126, no. 3, p. 477-487.

Other print sources

Studies of mercury and other contaminants:

Krabbenhoft, D.P. and Rickert, D.A., 1995, Mercury contamination of aquatic ecosystems: U.S. Geological Survey Fact Sheet 216-95, 4 p.

U. S. Environmental Protection Agency, 1992, National study of chemical residues in fish: Washington, D.C., Office of Science and Technology, EPA 823-R-92-008b. (For copies, write or call: USEPA, National Center for Environmental Publications & Information, P.O. Box 42419, Cincinnati OH 42419; 1-800-490-9198.)

World Wide Web sources

Effects of mercury on human health:

Agency for Toxic Substances and Disease Registry, 1995, ToxFAQs---Mercury: Atlanta, Ga., U.S. Department of Health and Human Services, Public Health Service, from URL, accessed May 21, 1997, HTML format.

Foulke, J.E., 1994, Mercury in fish---Cause for concern?: Washington, D.C., U.S. Food and Drug Administration, from URL, accessed May 21, 1997, HTML format.

Contaminants in the Columbia River Basin:

U. S. Environmental Protection Agency, 1996, Columbia River Basin contaminant
aquatic biota and sediment data: Seattle, Wash., U.S. EPA, Region 10, from URL, accessed May 21, 1997, HTML format.

Suggested citation

Erwin, M.L., and Munn, M.D., Are walleye from Lake Roosevelt contaminated with mercury?: U.S. Geological Survey Fact Sheet FS-102-97, on line at URL, accessed October 16, 1997.


This study was requested by the Lake Roosevelt Water Quality Council and was funded by Region 10 of the USEPA. The Spokane Walleye Club, the Spokane Tribe, and Terry Short, Moon Kim, Connie Dean, and Steve Goodbred of the USGS helped with fish collection. The USGS Toxics Substances Hydrology Program and National Water-Quality Assessment Program funded this fact sheet.

For more information, contact Dr. Munn:
U.S. Geological Survey
Water Resources Division
1201 Pacific Avenue, Suite 600
Tacoma, WA 98402
(253) 593-6510

For more information on the water quality of lakes in Washington State, see Washington State Department of Ecology web pages at

USGS Fact Sheet FS-102-97
by Martha L. Erwin and Mark D. Munn
August 1997

Water Resources of Washington State || U.S. Geological Survey
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