WASHINGTON – The Trump administration is on the verge of moving forward with a significant rollback of an Obama-era clean water regulation that has become a rallying cry for farmers and property-rights activists opposed to federal overreach.

The new proposal, whose details will be unveiled Tuesday morning by EPA Administrator Andrew Wheeler and other administration officials, is expected to ease government oversight of small bodies of water, undoing a regulation President Donald Trump has called "a massive power grab."

The new rule would replace an Obama administration regulation, known as the "Waters of the United States" rule that sought to expand federal protections to smaller rivers and streams.

Environmental advocates say the proposed rule could remove pollution and development protections from most U.S. waterways. But opponents of the Obama-era WOTUS rule say it unduly prevents property owners from being able to fully use their land because the rule's overly broad definition regulates ditches that temporarily flood as federally protected waterways.

It's also confusing because the rule is enforced in only 22 states, the District of Columbia, and the U.S. territories.

In one of his first acts as president, Trump signed an executive order in February 2017 to undo the clean water rule and instructed the EPA and the U.S. Army Corps of Engineers to come up with a new approach.

In a Roosevelt Room ceremony with farmers and lawmakers at the time, Trump called the rule "one of the worst examples of federal regulation."

The debate over the water rule was part of a larger political flash-point over environmental issues during the 2016 presidential campaign as Trump tried to appeal to rural Americans exasperated by federal regulations and the loss of property rights.

While the broader debate centered on climate change and clean air rules, the waters rule was nearly as polarizing because its broad application could affect farming, construction and other activities near federally regulated waters.

The issue has often come down to the definition of "navigable waters" under the Clean Water Act.

The Clean Water Act of 1972 makes it illegal to pollute "navigable" waters. Over the decades, disputes arose over the government's changing definition of "navigable" with opponents complaining the definition was too broad.

Two Supreme Court decisions in 2001 and 2006 came down on the side of landowners, ruling that ponds at the bottom of a gravel pit and a marsh miles from any lake or river were not navigable and thus not subject to the act.

Under the 2015 rule, those waters could include, for example, anything within a 100-year floodplain or within 4,000 feet of a high-tide mark.