The decision is an important one for government bodies that control local storm sewer systems.
In the case, the Los Angeles County Flood Control District operates a "municipal separate storm sewer system" a "drainage system that collects, transports and discharges storm water"
Because storm water is often heavily polluted, the Clean Water Act and its regulations require certain "operators to obtain a National Pollutant Discharge Elimination System permit before discharging storm water into navigable waters," the Supreme Court opinion said.
Despite the fact that the district had such a permit, the Natural Resources Defense Council Inc. and Santa Monica Baykeeper filed suit against the district and others under the Clean Water Act, "alleging, among other things, that water quality measurements from monitoring stations within the Los Angeles and San Gabriel rivers demonstrated that the district was violating the terms of its permit.
Reversing a lower-court decision, the opinion written by Justice Ruth Bader Ginsburg said, "The flow of water from an improved portion of a navigable waterway into an unimproved portion of the same waterway does not qualify as a 'discharge of a pollutant' under the CWA."
All the other justices signed on to Ginsburg's opinion, except for Justice Samuel Alito, who filed a separate opinion concurring in the judgment.