Common loons that stage during migration at Walker Lake, Nevada, were found to have elevated concentrations of mercury in their blood.  The source of the mercury was unknown, although fish from Walker Lake are known to contain moderate concentrations. Therefore, an investigation was initiated to determine the sources of mercury in the Walker River basin and the concentrations of mercury in Walker Lake tui chub of the size consumed by common loons to determine risk to this fish-eating species.  A total of 12 fish and 29 aquatic invertebrate samples were collected in 1999 to 2001 at 19 sites in the Walker River basin.  Mercury concentrations in aquatic invertebrate samples collected at sites downstream of historic mine sites, where mercury was used in precious metal recovery in the late 1800's, were often higher than at sites where no historic mining influences were present.  Mercury concentrations in tui chub from Walker Lake increased with size of the fish, with a major increase for fish greater than 25 centimeters in length.  Mercury concentrations in fish were below those associated with adverse effects to fish.  Mercury concentrations in larger tui chubs may be a risk to fish-eating birds, including common loons.  Data on mercury concentrations in stream sediment form the Walker River basin that were provided by the U.S. Geological Survey and the U.S. Environmental Protection Agency were examined in relation to the concentrations found in this study in aquatic invertebrates. These data sets suggested that mercury source areas included: an area of the Virginia Creek watershed, south of Bridgeport, California; several sites on the southeast side of the Sweetwater Range near the California-Nevada state line, which included areas along Sweetwater and Fryingpan Creeks; Bodie, California; and the nearby Aurora district in Nevada. Additional studies are need to further define mercury source areas for possible stabilization or cleanup. Additional information is also needed on common loons which include the following:  fall migration patterns and wintering areas to determine if the birds frequent known areas of mercury contamination; mercury exposure on the breeding grounds in Saskatchewan; and mercury in blood of loons using other Nevada lakes and reservoirs during migration to determine if Walker Lake is a significant source of mercury.

Learn More by Reading the Full Report: Wiemeyer, S.N., Mercury in Biota and Sediment in the Walker River Basin, Nevada and California, USFWS.  Reno FWO.  2002.

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