Scientists with the U.S. Geological Survey have found high levels of mercury in brown trout from Silver Creek, one of Idaho's most treasured trout streams.
The survey, funded by the Nature Conservancy, showed levels of mercury that are considered unhealthy for young children and women of child-bearing age.
State officials have already issued advisories to anglers for 10 other bodies of waters in the state and have tested 48 other lakes and reservoirs to determine just how widespread the mercury pollution is.
But finding high levels in fish taken from Silver Creek, a moving body of water, is especially troubling.
"We tend to expect this kind of thing in stagnant bodies of waters like lakes and reservoirs," said Kai Elgethun, Idaho's public health toxicologist. "It's surprising when you find this in a creek."
No one knows yet the source of the mercury. But Idaho Department of Environmental Quality officials, based on their own uncompleted statewide survey, suggest that it is being carried through the air.
"It seems to be widespread enough that air deposition is not the only source, but the major source," said Don Essig, a DEQ water scientist in charge of the state's mercury monitoring program.
State and Idaho National Laboratory scientists have evidence that mercury from mines in Nevada is carried into Idaho. A cement plant in Oregon also is a major source.
Elgethun and others are still assessing the Silver Creek information before the state will issue a formal health advisory. But the average mercury level found in 10 brown trout sampled, .48 parts per million, is above the safe level of 0.1, said Jim Vannoy, program manager at the Idaho Division of Public Health.
"At that point we would want people to limit the amount of fish they ate, especially women of reproductive age and children," Vannoy said.
The advisories in the 10 bodies of water recommend that pregnant women, children under 7 and the general public limit themselves to two meals a month to eight meals a month, depending on the level of mercury contamination. The 10 other waters are:
• Priest Lake.
• Lake Pend d'Oreille.
• Lake Coeur d'Alene.
• Brownlee Reservoir.
• Lake Lowell.
• Jordan Creek.
• C.J. Strike Reservoir.
• Salmon Falls Creek Reservoir.
• American Falls Reservoir.
• East Mill Creek.
Most of Silver Creek, especially the popular Silver Creek Preserve managed by the Nature Conservancy, is a catch-and-release stream, so the high mercury levels aren't a direct threat to people. But anglers are allowed to keep fish from some parts of the creek.
The Nature Conservancy funded the research because of its concerns about pollution in the Silver Creek ecosystem, said Dayna Gross, the preserve's manager. Idaho's Department of Environmental Quality has separately sampled 48 lakes and reservoirs statewide this year to get some idea what percentage of the state's waters are contaminated with mercury. They hope to have preliminary results by December, Essig said.
What they do know is that Salmon Falls Creek Reservoir, a popular walleye fishing lake on the Nevada border, has the highest level of mercury.
"It's a hot spot," Essig said.
In 2005, the discovery of high mercury levels in the reservoir prompted Idaho officials and environmentalists to press Nevada gold mines to reduce emissions of mercury, which accumulates in fish and can cause brain damage and learning disabilities in babies and young children.
Research conducted by the Idaho National Laboratory showed that mercury levels in the air south of Twin Falls rose 30 to 70 percent higher than normal levels when winds blew from the southwest, where the Nevada gold mines are located.
Silver Creek is 60 miles north of Salmon Falls Creek. It also lies downwind of another major mercury source, the Ash Grove Cement plant in Durkee, Ore., 100 miles west of Boise.
But the mercury could be in the soil and rock underlying the creek or it could even come from forest fires, which release mercury deposited from years of accumulation.
Whatever the source, Silver Creek's contamination adds to the growing concern state officials have expressed about the pollutant.
Gov. Butch Otter announced last month his intention to keep Idaho out of a Bush administration program that would cap mercury emissions from coal-fired electric plants but allow new plants to buy pollution credits from existing plants. Otter also endorsed DEQ's efforts to work with surrounding states to reduce mercury pollution, and he told DEQ Director Toni Hardesty to expand the effort.
Rocky Barker: 377-6484
