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Gold Rush mercury taints area fish

Dave Moller

A federal research chemist says mercury left in Sierra watersheds by Gold Rush miners could take hundreds of years to flush out naturally.

At a recent meeting of the Bear River Watershed Group, Charlie Alpers said the water is safe to drink in Nevada and Placer counties, but as the mercury moves through the food chain, it becomes the toxin methylmercury and is found in fish.

Consuming too many of those fish could cause neurological problems in people, Alpers said. His advice was to eat no more than one meal a week of fish caught in the Yuba, Bear and Deer Creek watersheds.

Alpers and his colleagues at the U.S. Geological Survey have been studying area watersheds for mercury since 1998. Their work led to a 2003 state warning to consume no more than four meals of fish per month from the local watersheds.

“It’s probably something you don’t want to do every day,” Alpers said about eating locally caught fish.

The USGS studies have found extreme mercury levels at Camp Far West Reservoir, which straddles the Nevada, Yuba and Placer county lines above Wheatland. The Nevada Irrigation District’s Combie Reservoir below Lake of the Pines “came in a close second” and needs follow-up study, Alpers said.

Rollins Reservoir off Highway 174 had mercury levels that were “quite a bit lower,” Alpers said. The cooler temperatures in the lake may be the reason, he said.

A new Bear River watershed study that is tracing levels of mercury toxins in the food chain will come out shortly, Alpers told a Higgins Community Center audience on Tuesday night. Readings have been taken from plankton, insects, slugs and fish for that study.

Sampling sites have included spots along Camp Far West, Combie, Rollins and the Dutch Flat reservoirs. Stream samplings have been taken on Greenhorn Creek in the You Bet Road area.

Alpers said the studies have come to several conclusions.

– “Mercury contamination is pervasive in gold mining areas” with more coming from placer than hard rock mines. He estimated that through the years, almost 13 million pounds of mercury were left in the Sierra by gold miners.

– Only 1 percent of the mercury left behind has turned into the toxic methylmercury. If that figure was 10 percent, the danger of consuming fish would rise dramatically.

– Contaminated sediments in foothill lakes and flood plains are likely to be long-term sources of mercury to the environment “so the benefits of cleaning up mine sites by be a long time coming.”


– ca.water.usgs.gov/mercury

This federal U.S. Geological Survey site has the findings and fish consumption warnings from the mercury survey done in the Yuba River, Bear River and Deer Creek watersheds.


This California environmental health department site has information about mercury in fish and its dangers.

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