This was posted in r/Keep_Track but I wasn't able to link it here. I highly recommend following that sub if you aren't already. Kavanaugh joined the dissent with Kagan, Sotomayor, and Jackson.

Kavanaugh writes:

I write separately because I respectfully disagree with the Court’s new test for assessing when wetlands are covered by the Clean Water Act. The Court concludes that wetlands are covered by the Act only when the wetlands have a “continuous surface connection” to waters of the United States—that is, when the wetlands are “adjoining” covered waters. Ante, at 20, 22 (internal quotation marks omitted). In my view, the Court’s “continuous surface connection” test departs from the statutory text, from 45 years of consistent agency practice, and from this Court’s precedents. The Court’s test narrows the Clean Water Act’s coverage of “adjacent” wetlands to mean only “adjoining” wetlands. But “adjacent” and “adjoining” have distinct meanings: Adjoining wetlands are contiguous to or bordering a covered water, whereas adjacent wetlands include both (i) those wetlands contiguous to or bordering a covered water, and (ii) wetlands separated from a covered water only by a man-made dike or barrier, natural river berm, beach dune, or the like. 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. Therefore, I respectfully concur only in the Court’s judgment…

The difference between “adjacent” and “adjoining” in this context is not merely semantic or academic. The Court’s rewriting of “adjacent” to mean “adjoining” will matter a great deal in the real world. In particular, the Court’s 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, with negative consequences for waters of the United States. For example, the Mississippi River features an extensive levee system to prevent flooding. Under the Court’s “continuous surface connection” test, the presence of those levees (the equivalent of a dike) would seemingly preclude Clean Water Act coverage of adjacent wetlands on the other side of the levees, even though the adjacent wetlands are often an important part of the flood-control project. See Brief for Respondents 30. Likewise, federal protection of the Chesapeake Bay might be less effective if fill can be dumped into wetlands that are adjacent to (but not adjoining) the bay and its covered tributaries. See id., at 35. Those are just two of many examples of how the Court’s overly narrow view of the Clean Water Act will have concrete impact…

The scientific evidence overwhelmingly demonstrates that wetlands separated from covered waters by those kinds of berms or barriers, for example, still play an important role in protecting neighboring and downstream waters, including by filtering pollutants, storing water, and providing flood control. In short, those adjacent wetlands may affect downstream water quality and flood control in many of the same ways that adjoining wetlands can.

Justice Kagan, joined by Justices Sotomayor and Jackson, wrote her own opinion castigating the majority for usurping Congress:

And still more fundamentally, why ever have a thumb on the scale against the Clean Water Act’s protections? The majority first invokes federalism. See ante, at 23–24. But as JUSTICE KAVANAUGH observes, “the Federal Government has long regulated the waters of the United States, including adjacent wetlands.” Post, at 11. The majority next raises the specter of criminal penalties for “indeterminate” conduct. See ante, at 24–25. But there is no peculiar indeterminacy in saying—as regulators have said for nearly a half century—that a wetland is covered both when it touches a covered water and when it is separated by only a dike, berm, dune, or similar barrier. (That standard is in fact more definite than a host of criminal laws I could name.) Today’s pop-up clear-statement rule is explicable only as a reflexive response to Congress’s enactment of an ambitious scheme of environmental regulation. It is an effort to cabin the anti-pollution actions Congress thought appropriate. See ante, at 23 (complaining about Congress’s protection of “vast” and “staggering” “additional area”). And that, too, recalls last Term, when I remarked on special canons “magically appearing as get-out-of-text-free cards” to stop the EPA from taking the measures Congress told it to. See West Virginia, 597 U. S., at – (dissenting opinion) (slip op., at 28–29). There, the majority’s non-textualism barred the EPA from addressing climate change by curbing power plant emissions in the most effective way. Here, that method prevents the EPA from keeping our country’s waters clean by regulating adjacent wetlands. The vice in both instances is the same: the Court’s appointment of itself as the national decision-maker on environmental policy.

So I’ll conclude, sadly, by repeating what I wrote last year, with the replacement of only a single word. “[T]he Court substitutes its own ideas about policymaking for Congress’s. The Court will not allow the Clean [Water] Act to work as Congress instructed. The Court, rather than Congress, will decide how much regulation is too much.” Id., at ___ (slip op., at 32). Because that is not how I think our Government should work—more, because it is not how the Constitution thinks our Government should work—I respectfully concur in the judgment only.