Kurt Hildebrand/Nevada Appeal The Carson River in Dayton is part of a 50-mile stretch between Carson City and Lahontan Reservoir contaminated with mercury - a historic remnant of the Comstock mining era. This stretch is Nevada's only Superfund site.
The Carson River and all that it feeds into have been contaminated with mercury ever since 19th century miners released some 7,200 tons of the toxic metal into the river nearest the Comstock mines.
A 50-mile stretch from Carson City downstream to Lahontan Reservoir is Nevada's only Superfund site.
Miners used mercury to draw gold and silver ores out of the worthless dirt and rock that surrounded them. A percentage of mercury was lost when the gold and silver were removed. The lost mercury went with the water, down the Carson River.
There's still a lot of good fishing in places along the Carson River system, such as the Lahontan Reservoir. But while those fish are good for catching, they should not be eaten.
"We advise people not to eat anything from (fishing spots) below Dayton," said Nevada Department of Wildlife biologist Mike Sevon.
But the state still encourages fishing throughout the Carson system. The department stocks Lahontan with several species of game fish. The waterways are promoted as a valuable sport-fishing resource, perfect for the catch-and-release method. As bad as it might be for humans, mercury does nothing to take the fight out of the fish.
Once in water, mercury starts turning toxic and builds up in fish. The U.S. Food and Drug Administration considers fish with a level of 1 part per million unsafe for human consumption. The department becomes concerned about fish-eating safety when levels climb above .5 part per million.
Fish in Carson River-fed lakes and wetlands are well above that, especially in the area's most popular water recreation spot.
Sevon called the fish at Lahontan Reservoir "world-class mercury carriers."
Since 1915, when the Lahontan Dam was completed, the reservoir has acted like a "mercury sink," Sevon said.
The average Lahontan fish over 12 inches in length has 3.24 parts per million mercury.
According to the Environmental Protection Agency, a walleye caught in the lake in 1998 had a record-high 16 parts per million mercury.
Investigations in the river are continuing. Once complete, the costs and benefits of cleaning up the mercury will be determined, according to the agency's Web site.
Contact Cory McConnell cmcconnell@lahontanvalleynews.com