High mercury levels found in trout from Silver Creek

BOISE – Trout in one of Idaho’s most famed fishing destinations are contaminated with such high levels of mercury that they are considered unsafe to eat, a study by the U.S. Geological Survey has found.

A sampling of 10 brown trout in central Idaho’s Silver Creek found the fish contained an average mercury level of 0.48 parts per million.

The safe level is 0.1 ppm, Jim Vannoy, program manager at the Idaho Division of Public Health, told the Idaho Statesman.

Some of the fish were taken from The Nature Conservancy’s Silver Creek Preserve, a fly-fishing destination that draws anglers from around the nation.

“We’re very concerned about it, obviously,” Dayna Gross, preserve manager, said Wednesday. “There’s a call to action to do more monitoring to see where it’s coming from.”

She said Silver Creek gets its water from springs, and those springs are replenished mainly from the Big Wood River, part of which disappears underground. She also said irrigation water taken from the Big Wood percolates back underground into the springs that feed the creek.

Gross said the tissue samples were taken from the trout in June, and the results released about two weeks ago. She said studies in 2001 and 2004 did not look at mercury levels.

“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.”

A formal health advisory has not yet been issued for Silver Creek, but state officials have issued such warnings to anglers to limit eating fish in 10 other water bodies that span the state because of high mercury levels.

They are Priest Lake, Lake Pend d’Oreille and Lake Coeur d’Alene in North Idaho; Brownlee Reservoir and Lake Lowell in western Idaho; Jordan Creek and C.J. Strike Reservoir in southwestern Idaho; Salmon Falls Creek Reservoir in south-central Idaho: and American Falls Reservoir and East Mill Creek in southeastern Idaho.

Don Essig, a water scientist with the state Department of Environmental Quality, said an uncompleted statewide survey suggests the mercury is being carried into the state through the air.

“It seems to be widespread enough that air deposition is not the only source, but the major source,” he said.