The Environmental Protection Agency on Thursday finalized a repeal of Obama-era water protections in a battle of regulatory ping pong that experts say will take new strategies to solve.

At issue is the 2015 Waters of the United States rule, which expanded the types of waterways that can receive federal protections under the Clean Water Act. Republicans sharply criticized the rule, characterizing it as a federal overreach that would regulate bodies of water as small as puddles, which it did not. Twenty-two states the District of Columbia and U.S. territories follow the 2015 rule, while the rest follow guidance dating back to the Reagan administration.

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