Mercury in its most lethal form concentrates where the Carson River enters Lahontan Reservoir, a report released by the U.S. Geological Survey confirms.
According to the report, titled "Methylmercury in water and bottom sediment along the Carson River System, Nevada and California, September 1998," methylmercury reaches its highest concentration in the delta.
Methylmercury is produced by bacteria and is a neurotoxin that is particularly dangerous to children.
The mercury is the result of 19th century mining, which used it to process gold.
It is washed out of old mines and tailings piles and into the river, where some is converted to methylmercury.
A three-day reconnaissance in 1998 revealed that while methylmercury in the water reaches a high point just before entering Lahontan Reservoir, the amount in the sediment is highest at two places in Stillwater.
"In bottom sediment at 14 sampling sites, the maximum concentrations, were found in two agricultural drains entering the Stillwater National Wildlife Refuge," Ray J. Hoffman, a Survey hyrdologist.
The levels of methylmercury in the river bottom increases steadily until about Fort Churchill when it drops off dramatically. The level spikes again in Stillwater.
A health advisory posted along the Carson River from Dayton to Lahontan Dam recommends that no game fish or carp be consumed from the river due to mercury.
There is no Nevada standard for methylmercury.
Karen Thomas of the U.S. Geological Survey pointed out that the study was based on a brief trip.
"This was a one-time shot. We did a reconnaissance in the fall of 1998. This is a reflection of what was in the river on those three days.
She said the Survey and the Environmental Protection Agency are working on a long-term study of the river.
"The EPA needs to make a decision about the mercury for their Superfund program," she said.
"It's important to look at what's entering Stillwater," she said. "I think the most interesting part of the study is looking at the data."
The three-day survey focused on 19 sites along the Carson River from Markleeville to Stillwater.
The report is available for inspection at the U.S. Geological Survey offices in Carson City, 333 W. Nye Lane, Room 103 and public libraries in Carson City, Fallon and Minden.
