WASHINGTON – The Trump administration is 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, unveiled Tuesday morning by acting EPA Administrator Andrew Wheeler and other administration officials, would ease Washington's 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 expanded federal protections to smaller rivers and streams.

Environmental advocates warn the proposed rule could remove pollution and development protections from most U.S. waterways and pose far-reaching effects on the safety of the nation's tap water for more than 100 million Americans.

“Even a child understands that small streams flow into large streams and lakes – which provide drinking water for so many Americans,” said Craig Cox, senior vice president for agriculture and natural resources for the Environmental Working Group. “By removing safeguards and allowing industry to dump pollutants into these water sources, Trump’s EPA is ensuring more contamination challenges for utilities and dirtier water for their customers.”

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.

“The old rule put Washington in control of ponds, puddles, and prairie potholes," said Wyoming GOP Sen. John Barrasso, who chairs the Environment and Public Works Committee. "The regulation was so confusing that property owners and businesses could not determine when permits were needed."

The crux of the rollback is a change in how "navigable waterways" are defined under the Clean Water Act.

The 2015 definition crafted under President Barack Obama would narrow considerably under Trump, a move that Wheeler told reporters would make it "clearer and easier to understand ... that will result in significant cost savings, protect the nation's navigable waterways, and reduce barriers to important economic and environmental projects."

Wheeler cited the Missouri Farm Bureau, which launched a "Ditch the Rule" campaign opposing the 2015 proposal because it was concerned the Obama-era definition was so broad it could apply to almost every acre in the state.

The Obama administration "claimed it was in the interest of water quality but it was really about power, power in the hands of the federal government over landowners," Wheeler said.

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

Under Trump's proposed rule, federal protections would remain for major waterways, rivers, tributaries, wetlands adjacent to federally protected waterways, certain lakes and ponds, reservoirs, and ditches used for navigation or affected by the tide.

States would oversee most ditches, terrain that fills with water during or in response to rainfall, certain wetlands that have been used to grow crops, stormwater control ponds, and water and wastewater treatment systems. Additionally, groundwater would not be federally protected, an exclusion Wheeler said that was never supposed to be included.

Wheeler disputed claims by environmental groups that the rule would remove federal oversight from at least 60 percent of the nation's waterways. But EPA officials also could not say what percentage would lose those protections.

Delaware Sen. Tom Carper, the top Democrat on the Environment and Public Works Committee, said the rollback would send the country back to a time when environmental protections were few and far between.

"Back then, the Cuyahoga River in Cleveland, Ohio, was so polluted that it actually caught on fire. Polluters were allowed to dump toxic waste into our waterways without consequence. Garbage littered our shores," Carper said. "It isn’t just a coincidence that this is no longer the reality in our country."

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 flashpoint 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.

Wheeler said he wants the rule to reflect the court rulings.

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