The justices ruled that the agency cannot impose generic prohibitions against violating water quality standards.

The Supreme Court limited the Environmental Protection Agency's ability to regulate water pollution in a ruling that has raised alarms among climate activists.

By a 5-4 vote, the court's conservative majority ruled that the Environmental Protection Agency overstepped its authority under the Clean Water Act with water pollution permits that contain vague requirements for maintaining water quality. The decision is the latest in which conservative justices have reined in pollution control efforts.