The United States Supreme Court decided last week in Sackett v. Environmental Protection Agency that a word does not mean what the dictionary, Congress, or two federal agencies have for 45 years understood it to mean.

The word in question is “adjacent,” and the context is when an “adjacent wetland” is a “water of the United States” (WOTUS) under the Clean Water Act (CWA). Five justices decided that “adjacent” means “adjoining” or “touching,” while four justices thought it should also mean “nearby.” As a result, millions of acres of wetlands will lose CWA protection.

The decision is groundbreaking in impact only; the legal foundation was laid in 2006 with the Court’s 4-1-4 split decision in Rapanos v. United States. Two tests emerged from Rapanos for determining whether wetlands were WOTUS: Justice Scalia’s “relatively permanent” test garnered a four-justice plurality, but Justice Kennedy’s “significant nexus” test became the swing vote despite arising from a single-justice concurrence. After Rapanos, most federal courts settled on significant nexus as the test. The EPA and the Army Corps of Engineers (the Corps), the two agencies that administer the CWA, issued their own WOTUS rules under the Obama, Trump, and Biden administrations with the significant nexus test as the foundation. However, each rule was struck down in the courts and otherwise repealed and replaced by the succeeding administration, furthering the uncertainty around the WOTUS definition and the extent of federal jurisdiction under the CWA.

With Sackett, a five-justice majority elevated Justice Scalia’s plurality opinion in Rapanos to the law of the land. While all nine justices concurred in the judgment reversing the Ninth Circuit’s application of the significant nexus test, the justices split over the definition of “adjacent.” Four justices joined a concurring opinion written by Justice Kavanaugh that would have applied the broader definition of “adjacent” to include wetlands near a navigable body of water based on 1977 CWA amendments, the Court’s precedent, longstanding agency practice, and dictionary definitions that unambiguously stated that the word “adjacent” is broader than and distinguished from “adjoining.” Justice Alito, writing for the majority, acknowledged that “[d]ictionaries tell us that the term ‘adjacent’ may mean either ‘contiguous’ or ‘near,’” but nevertheless decided that he could define the word better than the dictionary. Justice Alito’s concern about “an elephant hiding in a mousehole” of the CWA language was overstated; the majority simply chose the narrower definition.

And so, as it now stands after Sackett, federal jurisdiction under the Clean Water Act extends to only those wetlands that have a continuous surface connection to (are adjoining or touching) bodies of water that constitute “waters of the United States” (a relatively permanent body of water connected to traditional interstate navigable waters) such that the wetlands are as a practical matter indistinguishable from the waters, making it difficult to determine where the water ends and the wetland begins.

The result is a near-complete removal of CWA coverage for upstream waters and wetlands physically separated from a WOTUS, such as by “a man-made dike or barrier, natural river berm, beach dune, or the like.” Justice Kavanaugh highlighted the “[s]ignificant repercussions for water quality and flood control” as well as the regulatory uncertainty that the Court’s decision would create. Indeed, the decision will have far-reaching impacts beyond Corps permitting to fill wetlands (the specific permitting issue in the case). For instance, the entire National Pollutant Discharge Elimination System (NPDES) permitting system governing construction and industrial activities and municipal stormwater systems will have to be recalibrated to determine basic eligibility.

Justice Kagan, in a concurring opinion joined by the Court’s three left-leaning justices, called the majority’s opinion “a reflexive response to Congress’s enactment of an ambitious scheme of environmental regulation” and derided “the Court’s appointment of itself as the national decision-maker on environmental policy.” Reiterating her concern from last term in West Virginia v. EPA, where the Court limited the EPA’s ability under the Clean Air Act to impose certain carbon emission limits on power generation facilities, she noted that a broad term is not the same as a vague term and denounced the majority for choosing a narrow definition to fit its desired policy preference.

Individual states will be left to fill the coverage gap for wetlands protection. In Massachusetts, local conservation commissions already take on this responsibility under the Wetlands Protection Act, G.L. c. 131, § 40, and local wetlands protection ordinances. The Department of Environmental Protection (MassDEP) has authority over the prevention, control, and abatement of water pollution under the Massachusetts Clean Waters Act, G.L. c. 21, §§ 26 et seq., but has traditionally taken a secondary role to the EPA’s regulation under the CWA. MassDEP may seek to expand its role under state law to account for any lapse in permitting due to changes in federal jurisdiction. In the short term, some members of the regulated community may see their permitting obligations lifted, and the process for determining permit eligibility will at least be a little clearer.