The Supreme Court's decision is the latest in which conservative justices have reined in pollution control efforts.

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

But over the past 50 years, some places have occasionally run afoul of the act. In San Francisco, the wastewater system discharges a mix of sewage and stormwater into the bay during major storms, often causing bacteria levels to exceed EPA regulatory standards .