Mercury Found in Bass From Sierra Watershed

A federal report released Monday says that health advisories may soon be issued for bass caught in two sparkling Sierra watersheds tainted by mercury from the Gold Rush.

The U.S. Geological Survey said samples taken last fall from reservoirs and streams in Nevada, Placer and Yuba counties show elevated levels of mercury in a variety of fish.

Concentrations in bass ranged up to 1.5 parts per million, well over the Food and Drug Administration’s limit of 1 ppm for commercial seafood.

Concentrations reached 0.75 ppm in channel catfish, 0.41 in sunfish, 0.43 in brown trout and 0.38 in rainbow trout--all above the 0.3 level that California considers indicative of the need for further study.

All told, 141 mercury samples were taken from fish caught last September and October in the Bear River and South Yuba River watersheds.

The mercury is left from the era when forty-niners used it to separate gold from ore. Much of the silvery, liquid metal slopped from sluice boxes into the waterways of the Sierra.

Mercury in the water is absorbed by microscopic bacteria and transformed into an organic form known as methyl mercury. It then works its way up the aquatic food chain from tiny invertebrates to small fish, finally concentrating in the largest fish, such as bass.

Formal health advisories probably won’t be issued for at least a year, but local officials are worried about the economic impact on a region heavily dependent on outdoor recreation and tourism.

Nationwide, mercury-tainted fish have prompted advisories at 1,900 lakes and estuaries. Thirteen of these advisories have been issued in California, several of them in the delta of the Sacramento River.