The U.S. Supreme Court’s new opinion in Sackett v. EPA greatly narrows federal regulation of wetlands under the Clean Water Act (CWA) by holding that only wetlands “indistinguishable” from adjacent “waters of the United States” (WOTUS) may be subject to federal jurisdiction.

The Court’s return to the “contentious and difficult task” of defining WOTUS (as Justice Samuel Alito’s majority opinion puts it), not only greatly restricts current federal authority over wetlands under the CWA, but it also raises questions for other portions of the Biden-era WOTUS rule.

Although all nine Justices on the Court agreed that the specific wetland at issue —a residential lot on the opposite side of a 30-foot road from an unnamed tributary of a creek feeding into Idaho’s Priest Lake—was not a WOTUS, the majority opinion penned by Justice Alito was joined only by Chief Justice John Roberts and Justices Clarence Thomas, Neil Gorsuch and Amy Coney Barrett; the remaining four Justices agreed only with the overall holding.

The majority overturned EPA’s determination that the case lot’s proximity to a “roadside ditch” occasionally feeding into a creek running to the intrastate Priest Lake satisfied the WOTUS standard, making direct reference to Antonin Scalia’s plurality opinion in 2006. Justice Scalia wrote that the definition of “waters” in the CWA included only wetlands that are “indistinguishable from waters of the United States,” which occurs only when such wetlands have a “continuous surface connection to bodies that are [WOTUS] in their own right, so that there is no clear demarcation between ‘waters’ and ‘wetlands.’”

The majority found no merit to EPA’s policy argument that the ecological connection between a WOTUS and another adjacent, but distinguishable water may be strong enough to justify federal regulation of both waters, writing that “the CWA does not define the EPA’s jurisdiction based on ecological importance, and we cannot redraw the Act’s allocation of authority.”

In contrast, Justice Kavanaugh and Justice Kagan’s concurring opinions, despite agreeing that the case lot was not a WOTUS, both argued that the majority ignored the plain language of the CWA – finding that the CWA’s reference to “adjacent wetlands” required such waters to be “contiguous to or “touching.”

As Justice Kavanaugh, joined by Justices Kagan, Ketanji Brown Jackson and Sonia Sotomayor, wrote, “eight different administrations have recognized as a matter of law that the Clean Water Act’s coverage of adjacent wetlands means more than adjoining wetlands and also includes wetlands separated from covered waters by man-made dikes or barriers, natural river berms, beach dunes, or the like. That consistency in interpretation is strong confirmation of the ordinary meaning of adjacent wetlands.” Justice Kagan’s concurring opinion, also joined by Justices Jackson and Sotomayor, expressly agreed with Justice Kavanaugh’s arguments and asked, “still more fundamentally … why ever have a thumb on the scale against the Clean Water Act’s protections?”

The majority’s arguments signal trouble for other key provisions of the Biden Administration’s 2022 WOTUS rule, which has faced legal battles in dozens of states across the country since its adoption. Federal courts have already blocked EPA’s implementation of the rule’s WOTUS definition in 27 states, responding to challenges to language that would permit federal jurisdiction over other controversial waterbodies such as non-navigable interstate waters.

For individuals and businesses regulated under the CWA, the Sackett decision may provide, at least with respect to wetlands, some welcomed certainty after years of regulatory upheaval.