A wetland.

The Trump administration finalized repeal of the 2015 "Waters of the U.S." rule effective Dec. 23, reverting to previous regulations, according to a Federal Register notice EPA and the U.S. Army Corps of Engineers published Oct. 22.

The action, taken Sept. 12, is likely to be challenged in court.

"While we don't go looking for a fight, there's too much at stake for us to let this go," California Attorney General Xavier Becerra said. "We're prepared to defend the clean water rule."

The repeal was praised by the National Rural Electric Cooperative Association. "The 2015 rule would have increased costs and regulatory hurdles for electric co-ops to build and maintain critical infrastructure without providing meaningful environmental benefits," Jim Matheson, the group's CEO, said in a statement.

EPA Administrator Andrew Wheeler said the repeal of what he called the Obama administration's "overreach" set the stage for finalizing a revised definition of waters of the U.S. that he said would provide "greater regulatory certainty."

The administration's replacement proposal, released in December 2018, spells out six water-body types subject to Clean Water Act regulation and specifies that other water bodies would not be under the law's jurisdiction.

Under the proposal, wetlands would fall under the law's reach if they are adjacent to other jurisdictional waters such as lakes and rivers, or if they have a hydrologic surface-water connection to jurisdictional waters through inundations or via perennial or intermittent streams.

R.D. James, assistant secretary of the Army for Civil Works, said the repeal "reestablishes national consistency" in Clean Water Act regulation of activities affecting surface water bodies.

Since its adoption, implementation of the 2015 regulation had been complicated by numerous court cases challenging and defending it.

The 2015 rule was blocked by court action in 26 states and was in effect in 23 others, including California, Colorado, Oregon and Washington. In New Mexico, the rule's status was in question, since 10 counties in the state challenged it in court.

The 2015 rule sought to clarify the Clean Water Act's reach over water bodies, including tributary streams and wetlands.