Fish from lakes and reservoirs contain toxic chemicals in nearly every US state, posing a threat to human health and the environment. According to a study from the Environmental Protection Agency (EPA), mercury levels in game fish exceed recommended levels in 49 percent of US lakes and reservoirs. Polychlorinated biphenyls (PCBs) in game fish exceed recommendations in 17 percent of US lakes and reservoirs. The EPA says air emissions from burning fossil fuels, especially coal, cause mercury and other toxins to enter US water systems. It calls for stricter regulations to enforce the Clean Water Act.