Chief Justice John Marshall famously described the job of the courts: to “say what the law is.” The courts are supposed to read the law, not write it. Sometimes, however, the written law leaves much unanswered. At a certain point, while it is important that the Supreme Court adhere to the text written by Congress, it is even more important that it settle on an answer that tells Americans what the law is, and what it is not. That is what the Court did on Thursday in Sackett v. EPA.

The Clean Water Act (CWA), enacted in 1972, aimed to clean up the nation’s “navigable waters” by prohibiting “the discharge of any pollutant” into those waters and placing them under the dual enforcement jurisdiction of the Environmental Protection Agency and the Army Corps of Engineers. While it could have rested on the traditionally familiar definition of “navigable waters” developed in more than a century of court decisions dating back to Marshall’s time, Congress chose to more specifically (it thought) define them as “the waters of the United States, including the territorial seas” — WOTUS, in bureaucratic parlance. An awkwardly written 1977 amendment involving permits indicated that WOTUS should be read, at least in some cases, as “including wetlands adjacent thereto.”

History and common sense would suggest that, while Congress was trying to catch bodies of water flowing into the nation’s navigable waters, it never intended to completely abolish the connection between the regulated waters and a navigable body of water such as “the territorial seas.” To do so would read multiple words completely out of the statute, including the crucial term “navigable.” It would also conflict with the use of “waters” throughout the CWA to refer to traditional bodies of navigable water.

In 2017, we described what followed as “a textbook example of federal mission creep,” as bureaucrats and successive administrations asserted such broad jurisdiction that even wet grass could qualify. One notorious effort, the “migratory bird rule,” effectively held that wet patches were navigable waters if a bird could fly to them. Even the regulators admitted that it was impossible to find a limit to this rule.

Worse, the law left landowners in a perpetual state of uncertainty in which the only way to know what “waters” were covered by WOTUS was either to ask the government (usually producing a negative answer, but only after much expense and delay) or take one’s chances and possibly end up with crippling fines and jail time. The regulators have preferred to treat WOTUS as a sword of Damocles rather than a law, instructing field agents to make case-by-case decisions pursuant to voluminous manuals, often with major regional variations.

Nothing is more central to the rule of written law than that the law be certain and knowable. Ordinary citizens, especially when facing criminal penalties, must be able to determine what is criminalized and what is not. Instead, for half a century, WOTUS has defied all efforts at definition. The Supreme Court in 1985 ruled that WOTUS extended beyond bodies of water that were themselves navigable to those that “abut” them, and in 2001, it threw out the migratory-bird rule as going too far. But the 2006 Rapanos decision failed to settle on an actual rule, with a 4–4 split and Justice Anthony Kennedy in the middle, doing his thing with a lone opinion proposing a fuzzy “nexus” test.

The agencies have done no better; without a firm definition of the statutory boundary, the definition of WOTUS has ping-ponged back and forth depending upon which party is in power. In 2015, we described the Obama administration’s rule as a “297-page manifesto [that] manages to be as unclear as the cesspools the government imagines backyard ponds to be.” Even the liberal justices in Sackett could not muster the pretense that the agencies had applied a consistent reading of the statute informed by expertise rather than executive-branch policy.

In Sackett, the EPA argued that the Court should defer to the agency’s “broad and unqualified” reading of WOTUS, such that it might cover all the water in the country. The only limiting principle is a “nexus” test nowhere found in the statute, requiring an assessment of aggregate effects of all “similarly situated” waters on the local ecosystem of a body of water that is or could be navigable. Whatever that is, it is not law. All nine justices were unanimous in rejecting the EPA’s “nexus” test. The Court thus finally ruled in favor of property owners who had been fighting the agency for 19 years over whether they could move dirt and rock onto water that was on the opposite side of a road from a non-navigable creek that feeds into a once-navigable lake, on the theory that the aggregate effect of the Sacketts’ body of water when combined with an unconnected fen would harm the lake.

Justice Alito’s opinion for a five-justice majority in Sackett finally settled the definition of WOTUS, adopting the rule proposed by the four-justice plurality in Rapanos: “only those relatively permanent, standing or continuously flowing bodies of water forming geographical features that are described in ordinary parlance as streams, oceans, rivers, and lakes.” Adjacent waters “must be indistinguishably part of a body of water that itself constitutes ‘waters’ under the CWA,” a rule requiring “a continuous surface connection . . . so that there is no clear demarcation between waters and wetlands,” even if that connection is sometimes broken by “low tides or dry spells.”

This may not be the only possible reading of the CWA, but it makes the best sense of what Congress wrote in a way that is actually comprehensible as law and provides fair notice to citizens of what they may be jailed for doing. Justice Clarence Thomas, joined by Justice Neil Gorsuch, wrote separately to note that without some flow into plausibly navigable waters, the CWA would exceed long-recognized limits on the power of Congress to regulate interstate maritime commerce. Lest we forget, that is the grant of power that Congress used to justify the CWA.

The main fireworks in the case, which led Chuck Schumer to thunder against “this MAGA Supreme Court,” was that Justice Brett Kavanaugh joined the three liberals in arguing that the majority improperly defined “adjacent” waters to include only adjoining waters rather than those “separated from a covered water only by a man-made dike or barrier, natural river berm, beach dune, or the like.” That definition has more consistently been included in the agencies’ otherwise-shifting rules. As the majority noted, this argument assumes that the term “adjacent” in a minor amendment regarding permitting should be read to define “navigable waters” rather than merely illustrate that adjacent waters may be covered if the waters actually connect.

Fair-minded readers may disagree; Congress did the Court no favors in writing either the statutory definition or the amendment in a way that engendered half a century of uncertainty. But we think Justice Alito’s resolution has the virtue of clarity: It is much easier for owners of property to determine what waters adjoin navigable waters than to enter into disputations of what is or is not nearby enough to qualify. If Congress wishes to go further, we recommend that it use language that will not take 51 years to decipher. In the meantime, when reading a law that can deprive citizens of their liberty, the Court should err, if it must, on the side of clarity. It has left these waters murky for too long.