NPR obtained internal documents from the Environmental Protection Agency that show that the agency has long been allowing oil companies to release polluted water on an Indian reservation in Wyoming. Millions of gallons of waste are released every month, creating streams of waste which ends up in natural rivers. The federal government banned this kind of dumping in the 1970s, but they made an exception, a loophole for the arid West. States in the West, however, eventually set up their own regulations to prevent this kind of polluting. Indian reservations are regulated only by the EPA, so the practice still happens in places like the Wind River reservation in Wyoming.