The justices are hearing arguments on whether an Alaska gold mine can dump metal waste into a nearby lake.

A ruling in favor of the mining company could allow the Clean Water Act to be interpreted to allow mining waste to be dumped into waterways throughout the United States, said Tom Waldo, a lawyer with the environmental group Earthjustice.

"The whole reason Congress passed the Clean Water Act was to stop turning our lakes and rivers into industrial waste dumps," Waldo said. "The Bush administration selected the Kensington mine to test the limits of the Clean Water Act."

The U.S. Army Corps of Engineers issued a permit for waste disposal at the proposed Kensington mine north of Juneau in 2005. Under the plan, tailings — waste left after metals are extracted from ore — would be dumped into Lower Slate Lake.

Environmentalists sued to halt the practice, saying it would kill fish. A federal appeals court blocked the permit, saying the dumping is barred by stringent Environmental Protection Agency requirements under the Clean Water Act of 1972. The EPA had agreed to a regulatory change in the case defining "fill" as "tailings or similar mining-related materials."

The mine's owner, Coeur Alaska Inc., said tailings are inert sandy material, and that almost half of the tailings created by the mine would be recycled back into mine operations. The remaining tailings would be placed in a small unproductive lake, which the company called the best option for disposal.