This lawsuit is pretty straightforward. The Department of Justice, on behalf of the EPA, and the California Attorney General, on behalf of the SF Bay Regional Water Quality Control Board, filed a civil complaint in federal court against the City and County of San Francisco, alleging Clean Water Act violations spanning the last decade. Sierra Club

The basic accusation: SF's sewer system is a mess and the city has been dumping massive amounts of untreated sewage into public waters. On average each year since 2016, San Francisco has discharged more than 1.8 billion gallons of untreated sewage from its combined sewer systems into creeks, San Francisco Bay, and the Pacific Ocean — including areas popular for wading, swimming, surfing, kayaking, and fishing. Sierra Club

Why does this happen? San Francisco is served by a combined sewer systems that collect domestic sewage, industrial and commercial wastewater, and stormwater in the same pipes. During heavy rains, when the sewage treatment plants are at maximum capacity, combined sewage is discharged from near-shore outfalls to creeks, the Bay, and the Pacific Ocean without receiving disinfection treatment. Sierra Club On top of that, San Francisco's combined sewer system is in a state of disrepair, and the city's failure to properly operate and maintain them has led to additional sewage discharges. Sierra Club The EPA also complained that San Francisco has consistently failed to properly notify the public about the presence of untreated sewage at popular water recreation locations and overflows from manholes onto sidewalks and streets. Sierra Club

The city faces potential civil penalties of more than $66,000 per day for each violation. Wikipedia