Feel free to eat the fish from Silver Creek.
That was the message delivered by the Idaho Department of Health and Welfare on Tuesday, when it declared that it was lifting a fish consumption advisory for the Silver Creek watershed because of a laboratory error that had calculated elevated mercury levels.
The advisory was recommended in 2007 after a study commissioned by the Idaho chapter of The Nature Conservancy and carried out by the U.S. Geological Survey tested contaminant levels in a total of 20 brown trout.
A news release from Health and Welfare stated that the analysis, conducted by a U.S. Geological Survey mercury lab in Wisconsin, detected high levels of mercury, an element known to be especially harmful to pregnant women as well as to children. That led to the recommendation that people limit the amount of brown trout they eat from Silver Creek.
A fish advisory is issued when the level of contaminants reaches levels at which the benefits of eating fish are outweighed by the risk to health. Mercury is the most common environmental contaminant absorbed by fish that can affect people.
However, USGS staff in Boise noticed a problem when recently reviewing test results that showed a large drop in mercury levels of fish compared to the results from two years ago. That discrepancy raised a red flag, as mercury levels in fish tend to be relatively stable from year to year.
After being contacted by the USGS researchers, the lab that performed the original analysis reviewed its report and found a calculation error that overstated the mercury levels.
"This is one of Idaho's premier sport fisheries and is good news for the Silver Creek watershed," said Jim Vannoy, environmental health program manager overseeing the Idaho Fish Advisory Program.
However, Don Essig, water quality standards coordinator at the Idaho Department of Environmental Quality, said that while detection of the error means that it is safe to eat trout from Silver Creek, it does not mean that mercury is not present in the watershed.
During the 2007 research, preliminary investigations suggested that the presence of mercury could at least in part be attributed to industrial gold-mining operations in northern Nevada and to a concrete plant across the state line in Durkee, Ore. Both are upwind from Silver Creek and are known sources of airborne mercury.
"This report doesn't change how much mercury is going into Silver Creek," Essig said in an interview. "It just lets us know why the results were so high [in 2007]."
The issue of fish consumption wasn't an issue of concern in the upper stretches of Silver Creek through the preserve, which is a designated catch-and-release area. Only in select areas of the creek does the Idaho Department of Fish and Game allow anglers to keep fish.
"It was an unfortunate error, but the lab has assured us that they have implemented procedures to prevent this from happening again," Vannoy said in the release.
As an additional safety measure, Fish and Game took another sample of fish from Silver Creek last week and had those analyzed by the Idaho Bureau of Laboratories. Those samples showed mercury levels below what would necessitate an advisory and similar to the recalculated 2007 levels.
According to the release, the Idaho Fish Consumption Advisory Program reviewed its other fish advisories in the wake of the Silver Creek error and found that all other advisories remain supported by reliable data.
Jon Duval: firstname.lastname@example.org