FIGURES

1. Map of South Yuba River, Deer Creek, and Bear River watersheds, California, and locations of major historic gold mining

2. Map of fish sampling sites in the South Yuba River, Deer Creek, and Bear River watersheds California, 1999

3. Correlation plot of interlaboratory comparisons for mercury concentrations in fish tissue

4. Mercury concentration for fish collected from Lake Englebright, California, 1999. A, In relation to total length. B, In relation to total mass

5. Mercury concentration for fish collected from Scotts Flat Reservoir, California, 1999. A, In relation to total length. B, In relation to total mass

6. Mercury concentration for fish collected from Rollins Reservoir, California, 1999. A, In relation to total length. B, In relation to total mass

7. Mercury concentration for fish collected from Lake Combie, California, 1999. A, In relation to total length. B, In relation to total mass

8. Mercury concentration for fish collected from Camp Far West Reservoir, California, 1999. A, In relation to total length. B, In relation to total mass

9. Mercury concentration for stream fish samples collected from South Yuba River, Deer Creek, and Bear River watersheds, California, 1999. A, In relation to total length. B, In relation to total mass

10. Mercury concentration for all bass (Micropterus sp.) samples collected from reservoirs in the South Yuba River, Deer Creek, and Bear River watersheds, California, 1999. A, In relation to total length. B, In relation to total mass

TABLES

1. Fish sampling sites in the South Yuba River, Deer Creek, and Bear River watersheds, California, 1999

2. Summary of interlaboratory comparison data for mercury concentration in fish fillet samples from the South Yuba River, Deer Creek, and Bear River watersheds, California, 1999

3. Data for fish collected from Lake Englebright, California, 1999, including common name, mercury concentration, moisture content of fillet tissue, gender, total length, and total mass

4. Data for fish collected from Scotts Flat Reservoir, California, 1999, including common name, mercury concentration, moisture content of fillet tissue, gender, total length, and total mass

5. Data for fish collected from Rollins Reservoir, California, 1999, including common name, mercury concentration, moisture content of fillet tissue, gender, total length, and total mass

6. Data for fish collected from Lake Combie, California, 1999, including common name, mercury concentration, moisture content of fillet tissue, gender, total length, and total mass

7. Data for fish collected from Camp Far West Reservoir, California, 1999, including common name, mercury concentration, moisture content of fillet tissue, gender, total length, and total mass

8. Data for stream fish collected from the South Yuba River, Deer Creek, and Bear River watersheds, California, 1999, including common name, mercury concentration, moisture content of fillet tissue, gender, total length, and total mass

9. Range and mean values of mercury concentrations and length for selected fish species and locations within the South Yuba River, Deer Creek, and Bear River watersheds, California, 1999

ABSTRACT

Mercury that was used historically for gold recovery in mining areas of the Sierra Nevada continues to enter local and downstream water bodies, including the Sacramento Delta and the San Francisco Bay of northern California. Methylmercury is of particular concern because it is the most prevalent form of mercury in fish and is a potent neurotoxin that bioaccumulates at successive trophic levels within food webs. In April 1999, the U.S. Geological Survey, in cooperation with several other agencies the Forest Service (U.S. Department of Agriculture), the Bureau of Land Management, the U.S. Environmental Protection Agency, the California State Water Resources Control Board, and the Nevada County Resource Conservation District began a pilot investigation to characterize the occurrence and distribution of mercury in water, sediment, and biota in the South Yuba River, Deer Creek, and Bear River watersheds of California. Biological samples consisted of semi-aquatic and aquatic insects, amphibians, bird eggs, and fish.

Fish were collected from 5 reservoirs and 14 stream sites during August through October 1999 to assess the distribution of mercury in these watersheds. Fish that were collected from reservoirs included top trophic level predators (black basses, Micropterus spp.) intermediate trophic level predators [sunfish (blue gill, Lepomis macrochirus; green sunfish, Lepomis cyanellus; and black crappie, Poxomis nigromaculatus)] and benthic omnivores (channel catfish, Ictularus punctatus). At stream sites, the species collected were upper trophic level salmonids (brown trout, Salmo trutta) and upper-to-intermediate trophic level salmonids (rainbow trout, Oncorhynchus mykiss).

Boneless and skinless fillet portions from 161 fish were analyzed for total mercury; 131 samples were individual fish, and the remaining 30 fish were combined into 10 composite samples of three fish each of the same species and size class. Mercury concentrations in samples of black basses (Micropterus spp.), including largemouth, smallmouth, and spotted bass, ranged from 0.20 to 1.5 parts per million (ppm), wet basis. Mercury concentrations in sunfish ranged from less than 0.10 to 0.41 ppm (wet). Channel catfish had mercury concentrations from 0.16 to 0.75 ppm (wet). The range of mercury concentrations observed in rainbow trout was from 0.06 to 0.38 ppm (wet), and in brown trout was from 0.02 to 0.43 ppm (wet). Mercury concentrations in trout were greater than 0.3 ppm in samples from three of 14 stream sites. Mercury at elevated concentrations may pose a health risk to piscivorous wildlife and to humans who eat fish on a regular basis. Data presented in this report may be useful to local, state, and federal agencies responsible for assessing the potential risks associated with elevated levels of mercury in fish in the South Yuba River, Deer Creek, and Bear River watersheds.

For additional information          Copies of this report can be 
write to:                           purcahsed from:

District Chief                      U.S. Geological Survey
U.S. Geological Survey              Information Service
Placer Hall, Suite 2012             Box 25286
6000 J Street                       Federal Center
Sacramento, CA 95819                Denver, CO 80225