Every stream tested in the U.S. found that fish were contaminated with mercury. The study by the U.S. Geological Survey is the most comprehensive look to date at mercury in the nation’s streams.
The news only gets worse. A landmark study by scientists from the U.S. Geological Survey (USGS) and universities in the U.S. and Australia has, for the first time, documented how escalating mercury-laden air emissions, chiefly from coal-fired electrical power plants in Asia, are being transformed into methylmercury. Methylmercury is a strong neurotoxin that is increasingly polluting the North Pacific Ocean and contaminating tuna, swordfish and other popular seafood.
http://water.usgs.gov/nawqa/mercury/majorfindings.html
http://www.ewg.org/newsrelease/Mercury-in-Fish-Predicted-To-Soar