Monitoring Mercury in Fish Tissue, Boise and Snake Rivers and Brownlee Reservoir

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To meet National Pollution Discharge Elimination System (NPDES) permitting requirements, the City of Boise will be responsible for collecting fish tissue samples for mercury analysis upstream of and downstream of their wastewater treatment facilities discharging to the lower Boise and Snake Rivers.

Mercury is a naturally occurring element that ultimately makes its way into aquatic ecosystems through the hydrologic cycle. Certain forms of mercury may be toxic to both aquatic life and to humans at elevated concentrations. Mercury in water enters the food chain through a natural process called methylation. In the right environments, methylmercury can accumulate in fish tissue and poses a risk to humans when we eat the contaminated fish.

USGS scientists will collect and analyze fish tissue for mercury from the Boise and Snake Rivers to help establish bioaccumulations factors (BAFs)—the ratio of mercury concentrations in water and mercury concentrations in fish tissue. These values provide information on the rate of transfer of mercury through the food chain and can be used to determine the mercury loading potential in these rivers.

All data will be quality assured and publicly available on the USGS National Water Information System Web Interface.

The data collected will also be provided to the Idaho Department of Health and Welfare, Idaho Fish Consumption Advisory Programto determine consumption advisories (if necessary) for sportfish caught from the lower Boise and Snake Rivers.