Coeur d'Alene Lake, Idaho

Though the water is clean, this lake is heavily contaminated. It is popular among the recreational boaters who are no doubt mostly unaware of what lies under them. At the bottom of the almost 50-square-mile lake is 75 million metric tons of contaminated sediment (replete with lead, zinc, cadmium, and other metals), deposited in the lake from the Coeur d'Alene Mining District upstream, part of which is now a 21-square-mile toxic area known as the Bunker Hill Mining and Metallurgical Complex Superfund site.