The Supreme Court ruled on Thursday that the Environmental Protection Agency’s ability to protect wetlands applied only to those that are indistinguishable from, and have a “continuous surface connection” to, larger lakes, oceans, streams and rivers. 

Environmentalists said the decision sharply limited the EPA’s ability to protect possibly more than half of the nation’s wetlands—amounting to millions of acres—from pollution under the Clean Water Act. 

The decision is a win for small property owners who don’t have teams of lawyers and consultants to navigate federal regulatory requirements, said Jonathan Adler, a professor of environmental, administrative and constitutional law at Case Western Reserve University. But it will also roll back important regulatory barriers for the real estate and construction industries, he said.

“Depending how state and local governments respond, this could have a big effect on wetland conservation in particular, and upon the ecosystem services that wetlands provide,” Adler said.

Environmental groups described the decision as a catastrophic limitation on clean water protections that undercuts the core purpose of the Clean Water Act. Enacted in 1972, the law provides the EPA and the Army Corps of Engineers with authority to protect “waters of the U.S.” and maintain their chemical, physical and biological integrity. 

“The Supreme Court ripped the heart out of the law we depend on to protect American waters and wetlands,” Manish Bapna, president and CEO of the Natural Resources Defense Council, said in a statement. “The majority chose to protect polluters at the expense of healthy wetlands and waterways. This decision will cause incalculable harm. Communities across the country will pay the price.”

The case, Sackett v. Environmental Protection Agency, centers on property owned by Chantell and Michael Sackett near Priest Lake, Idaho. After obtaining permits and beginning construction on their home in 2007, they were informed by the EPA that their property contained wetlands and they needed federal permits to continue work.

Construction of the home has been on hold ever since while the Sacketts appealed an EPA compliance order threatening tens of thousands of dollars in fines through the courts.

On Thursday, all nine of the court’s justices were unanimous in the decision that the Clean Water Act does not apply to the Sackett’s property and that the previous interpretation of “waters of the U.S.” was unworkable. The justices differed, however, in defining a new test.

According to the conservative majority opinion, written by Justice Samuel Alito and joined by Chief Justice John Roberts and Justices Clarence Thomas, Neil Gorsuch and Amy Coney Barrett, a wetland should only be covered by the law if it has a “continuous surface water connection” that makes it “indistinguishable” from a stream, ocean, river, or lake. 

This means that wetlands set back from a larger, navigable body of water would not be subject to federal protection, even if they are located along important floodplains or flood prone areas.

This test “narrows the Clean Water Act’s coverage of “adjacent” wetlands to mean only “adjoining” wetlands”, Justice Brett Kavanaugh wrote in a concurring opinion joined by Justices Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson. “By narrowing the Act’s coverage of wetlands to only adjoining wetlands, the Court’s new test will leave some long-regulated adjacent wetlands no longer covered by the Clean Water Act, with significant repercussions for water quality and flood control throughout the United States,” he warned.

Further, the test is sufficiently novel and vague that it could perpetuate regulatory uncertainty, he wrote.

The proper interpretation of “waters of the U.S.” has caused uncertainty for decades, with the Supreme Court’s previous test, outlined in the 2006 case, Rapanos v. United States, proving vague and largely unworkable. This interpretation extended federal protections to “relatively permanent” waters.

An Obama-era rule attempted to restore federal oversight to 60 percent of the nation’s waters in 2015, but this was struck down in nearly 30 states and later rescinded by former President Trump’s Navigable Waters Protection Rule. 

Thursday’s decision comes just five months after the EPA and the Army Corps finalized an updated definition based on scientific and technical recommendations.

But today’s ruling will send the EPA “back to the drawing board to revise their definition in light of what the court ruled,” Adler said. It appears stricter than the Rapanos decision, with which there was at least some talk of eligibility for so-called Chevron deference, he noted. This is a doctrine of judicial deference that requires a federal court to defer to the relevant agency’s reasonable interpretation of an ambiguous statute. “But I don’t see that kind of wiggle room in [Justice] Alito’s decision.”

No matter the uncertainty, this is a loss for the environment, the environmental law organization Earthjustice said in a statement. “All water is connected. Pollution that goes into wetlands can easily spread to lakes, rivers, and other drinking water sources,” it added.

The ruling is a second significant blow to environmentalists, after the Supreme Court severely curtailed the EPA’s powers to regulate climate change under the Clean Air Act last year. In response to this ruling, Congress largely turned to fiscal tools to limit greenhouse gas emissions.

“There are already a range of small environmental programs that are universal across species as a means of protecting wetlands,” Adler said. “I’ll be curious to see whether or not we see a similar shift in strategy at the federal level, because it would certainly be easier for Congress to increase spending and the funding for those sorts of programs than it would be for Congress to revise the Clean Water Act’s regulatory authority.”