In a 7-1 vote, the court reversed a federal appeals court ruling which held that muddy water running off roads used in industrial logging is the same as any other industrial pollution, requiring a Clean Water Act permit from the Environmental Protection Agency.
EPA itself disagreed with that court ruling, and Justice Anthony Kennedy said for the court that the agency's reading of its own regulations is entitled to deference from the court.
In any event, the agency has since issued a new regulation that removes any doubt that water from logging roads is the same as runoff from a farmer's field, not industrial pollution.
Justice Antonin Scalia dissented, saying that the court gives EPA and other agencies the authority to say what their rules mean "for no good reason."
Justice Stephen Breyer did not take part in the case because his brother, U.S. District Judge Charles Breyer, was appointed to sit on the appeals court panel that issued the ruling overturned Wednesday.
The consolidated cases are Decker v. Northwest Environmental Defense Center, 11-338, and Georgia-Pacific West v. Northwest Environmental Defense Center, 11-347.