The USGS said about a quarter of the fish were found to contain mercury at levels exceeding the U.S. Environmental Protection Agency's criterion for the protection of people who consume average amounts of fish. More than two-thirds of the fish exceeded the EPA level of concern for fish-eating mammals, the scientists said.
"This study shows just how widespread mercury pollution has become in our air, watersheds, and many of our fish in freshwater streams," said Secretary of the Interior Ken Salazar. "This science sends a clear message that our country must continue to confront pollution, restore our nation's waterways, and protect the public from potential health dangers."
The USGS study found some of the highest levels of mercury in fish in the "blackwater" streams in North and South Carolina, Georgia, Florida and Louisiana. High levels of mercury in fish also were found in relatively undeveloped watersheds in the Northeast and the Upper Midwest. Elevated levels were noted in areas of the Western United States affected by mining.
The full USGS report is available at http://pubs.usgs.gov/sir/2009/5109/pdf/sir20095109.pdf.