High mercury levels continue to plague fish in Emigrant Lake, as well as pose a human health risk.




The Oregon Department of Human Services rates Emigrant's mercury levels as "very high."




ODHS recommends that pregnant women, women of childbearing age, people with liver or kidney damage and children under the age of 6 avoid eating fish from the reservoir. Healthy adults should limit their consumption to eight ounces a month. The warning excludes rainbow trout.




Mercury is not a new problem for the lake. Tests by ODHS in 2005 found high levels of mercury in the lake's smallmouth bass and rainbow trout populations. ODHS issues advisories for all bodies of water that show mercury levels exceeding 0.35 parts per million. Samples taken from Emigrant Lake in the fall of 2005 showed levels of 0.82 parts per million.




Other waters in Oregon with very high levels of mercury include Cottage Grove Reservoir, Antelope Reservoir and Owyhee River.




"It really is a fairly widespread problem," said Southern Oregon University biology professor Michael Parker.




Mercury can come from various sources, both naturally occurring and manmade. The exact source of the lake's mercury remains unknown. Emigrant Lake is the only body of water sampled in Jackson County to carry such a high mercury level.




According to Steven Petrovic, an associate professor of chemistry at Southern Oregon University, inorganic mercury occurs naturally in the form of cinnabar deposits. This type of mercury can find its way into lakes and waterways, but usually in small amounts.




Organic mercury is more dangerous, and is also more fat soluble than inorganic mercury. As a result, organic mercury tends to bioaccumulate up the aquatic food chain. Bioacculumation occurs because organisms high in the food chain consume many other organisms, along with the mercury they contain, throughout their lives.




Some microbes can also convert naturally occurring inorganic mercury into organic forms. According to Parker, the sediments in Emigrant Lake are conducive to the growth of such microbes. However, Parker said the mercury contamination in the lake does not pose a significant risk to swimmers, as accumulates up the food chain, not in the water.




To avoid mercury consumption, ODHS recommends the removal of skin, organs, eggs and fatty tissue from wild caught fish. Mercury can cause nervous system damage, and symptoms of mercury poisoning include vision loss, hearing loss and tremors. Mercury can affect fetuses and accumulate in breast milk.




According to ODHS, most mercury in Oregon's water comes from natural geologic processes. Mining, pesticide use and other human factors can also contribute to high mercury levels in the environment.




The 2008 Oregon Fishing Regulations handbook contains information about mercury levels in Oregon's lakes and waterways, along with consumption guidelines. The handbook is available online from the Oregon Department of Fish and Wildlife at .