The U.S. Environmental Protection Agency says California is falling short on preventing water pollution, largely because of its problem with homelessness in big cities such as Los Angeles and San Francisco.

EPA Administrator Andrew Wheeler outlined the complaints Thursday in a letter to California Gov. Gavin Newsom. Wheeler is demanding a detailed plan for fixing the problems within 30 days.

The letter says “piles of human feces on sidewalks and streets” could cause water contamination. It criticizes San Francisco for routinely discharging inadequately treated sewage into the Pacific Ocean.

Wheeler says if the state doesn’t meet its responsibilities, EPA will have to take action.

The letter escalates a feud between the Trump administration and California, a predominantly Democratic state that has fought the administration’s efforts to weaken environmental regulations.

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