The Environmental Protection Agency recently said it would repeal a rule that weakened pollution controls for wetlands and streams enacted by the Trump Administration.

The so-called “Waters of the United States” rule enacted in the Obama era extended environmental protections for millions of streams, marshes, and other bodies of water across the nation. The EPA said it has found that the rollback of the protections under Trump caused “significant environmental degradation.”

The problem is most acute in arid states in the southwest, where nearly all of more than 1,500 streams lost environmental protections, according to the E.P.A. The agency stands a greater chance of defending the more stringent rules against legal challenges by moving forward early in Biden’s term, said a professor of environmental law at New York University interviewed in a New York Times report.

The original Obama-era rule extended the range of bodies of water subject to the 1972 Clean Water Act. It protected about 60% of the nation’s waterways, limiting discharge of fertilizers, pesticides, and industrial chemicals into those waters. It also limited development close to protected waterways.