The Supreme Court has unanimously sided with Los Angeles area governments that are fighting a lawsuit over pollution from urban storm water runoff.

Justice Ruth Bader Ginsburg wrote for the court in a narrow holding Tuesday that the federal appeals court in San Francisco wrongly ruled for environmentalists in their lawsuit against the Los Angeles Flood Control District. At issue is responsibility for billions of gallons of polluted water that flow into the Los Angeles and San Gabriel rivers, and eventually the Pacific Ocean, after heavy rainfalls.

The environmental groups say levels of bacteria from animal feces and toxic metals frequently exceed water quality standards.

The suit involved compliance with an older permit regulating water pollution. Ginsburg said a new permit more precisely monitors sources of pollution.