Conservative justices on the nation’s high court Thursday rolled back environmental protections in a ruling that advocates say could lead to unchecked pollution in more than half the wetlands in the US.

By a 5-4 vote, the Supreme Court said that wetlands are only protected by the Clean Water Act if they have a “continuous surface connection” to larger bodies of water.

The case stemmed from an Idaho couple’s grievance with federal officials who had required them to get a permit before building on a soggy portion of their property near Priest Lake, just south of the Canadian border.

In the court’s property rights championing opinion, Justice Samuel Alito jettisoned a 17-year-old protection to wetlands under the landmark 1972 water law.

Alito wrote that wetlands have to have a “significant nexus” to larger waterways to qualify for federal regulation, agreeing with opponents who said the 2006 decision that gave broad protection was vague and unworkable.

Although all nine justices agreed the wetlands on the couple’s property were not protected by the act, Conservative Brett Kavanaugh had joined the panel’s three liberal justices in arguing that the decision went too far in rewriting the nation’s primary water pollution-governing law.

The “new and overly narrow test may leave long-regulated and long-accepted-to-be regulable wetlands suddenly beyond the scope of the agencies’ regulatory authority,” Kavanaugh wrote, saying efforts to control flooding on the Mississippi River and protect the Chesapeake Bay could be threatened by the decision.

Dissenting justice, Justice Elena Kagan, compared the ruling to last year’s decision that limited the regulation of greenhouse gas emissions under the Clean Air Act, arguing the court had overridden Congress by appointing “itself as the national decision-maker on environmental policy.”

Manish Bapna, the chief executive of the Natural Resources Defense Counsel, called on Congress to amend the Clean Water Act to restore the protections.

“The Supreme Court ripped the heart out of the law we depend on to protect American waters and wetlands. 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,” Bapna said in a statement.

The ruling was expected to influence ongoing litigation over wetlands regulations that the Biden administration affected last year, which has been blocked in 26 states by two federal judges.

With Post wires