Scientists say water quality in the Coeur d'Alene and Spokane river basins in northern Idaho and eastern Washington state is improving due to ongoing efforts cleaning up one of the nation's largest Superfund sites.
The United States Geological Survey in a report released Monday says concentrations of cadmium, lead and zinc decreased significantly since the U.S. Environmental Protection Agency began the cleanup process in the 1990s.
However, the study also found that the concentration in some streams is above what's considered toxic to aquatic organisms.
It also found that Coeur d'Alene Lake annually receives about 5 tons of cadmium, 400 tons of lead and 700 tons of zinc. Some of that continues downstream into Washington.
Mining in the region before pollution controls resulted in the release of the toxic metals.