In 2022, when the US Supreme Court agreed to hear Sackett v. EPA, the Court indicated it would consider “the proper test” for determining when “wetlands” should be considered “waters of the United States” (WOTUS) “under the Clean Water Act, 33 U. S. C. § 1362(7).” On May 25, 2023, the Court decided Sackett, announcing that WOTUS “encompasses ‘only those relatively permanent, standing or continuously flowing bodies of water ‘forming geographic[al] features’ that are described in ordinary parlance as ‘streams, oceans, rivers, and lakes.’” The interior quote is taken from the plurality opinion in Rapanos authored by now-deceased Justice Scalia.

Scalia’s Reasoning Now Binding
A “plurality decision” is one that received the most votes for the winning side but whose reasoning is not adopted by a majority; a plurality opinion is not binding in future cases or on the other branches of government. With Sackett, Justice Scalia’s reasoning in Rapanos has a majority and is binding.

In Rapanos, Justice Kennedy (retired in 2018, replaced by Justice Kavanaugh) articulated a “significant nexus” test in his separate concurrence, which the lower court in Sackett (9th Circuit) used in its decision. All nine Supreme Court justices rejected the “significant nexus” test for determining when wetlands and other areas are WOTUS. However, only five (still a majority) adopted Justice Scalia’s reasoning.

Three Concurring Opinions
Justices Thomas and Gorsuch fully joined Sackett’s majority opinion and issued a concurrence saying the statutory terms “navigable” and “of the United States,” in addition to “waters,” similarly restrict the scope of WOTUS and federal regulatory power.

Four justices joined Justice Kavanaugh’s concurrence. Three of those justices issued yet another concurrence. These latter two concurrences assert that while the Court correctly rejected the “significant nexus” test, the Rapanos reasoning overly restricts regulatory authority.

To see the majority and concurring opinions https://www.supremecourt.gov/opinions/22pdf/21-454_4g15.pdf