President Donald Trump just signed an executive order to roll back President Barack Obama’s clean water rule. That environmental regulation was issued in 2015 to give the federal government authority to limit pollution in major bodies of water, rivers, streams, and wetlands.

The executive order directs the Environmental Protection Agency’s leader Scott Pruitt to initiate the lengthy legal process of rescinding and rewriting the rule, called Waters of the United States. That process could take longer than Trump’s first term, according to The New York Times.

The clean water rule was issued under the Clean Water Act of 1972. It was meant to expand the federal government’s authority to regulate pollution in smaller streams and rivers that flow into larger bodies of water like the Chesapeake Bay, Mississippi River, and Puget Sound. The rule gives protection to 60 percent of the US’s bodies of water, including wetlands.

Obama’s rule was attacked by oil and gas developers, farmers, pesticide and fertilizer makers, and golf course owners, which claimed the regulation infringes on property owners’ rights and is bad for the economy. In 2015, the American Farm Bureau Federation led a lawsuit against the rule, arguing it puts the burden on farmers to get a permit for using fertilizers near ditches and streams. The case has been in the courts ever since, and the rule has never actually been implemented.

Today’s executive order basically puts the legal case on hold, and directs the EPA to rework the rule. Environmental groups like the Center for Biological Diversity oppose Trump’s order, and claim it will hurt valuable habitat like wetlands, which are home to many endangered species at risk of extinction.

“Trump just put millions of acres of wetlands on the chopping block, and our wildlife and waters will suffer,” Kierán Suckling, executive director of the Center for Biological Diversity, said in a statement.

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