Syllabus
(a) The uncertain meaning of “the waters of the United States” has been a persistent problem, sparking decades of agency action and litigation. Resolving the CWA’s applicability to wetlands requires a review of the history surrounding the interpretation of that phrase. Pp. 6–14.
(1) During the period relevant to this case, the two federal agencies charged with enforcement of the CWA—the EPA and the Army Corps of Engineers—similarly defined “the waters of the United States” broadly to encompass “[a]ll … waters” that “could affect interstate or foreign commerce.” 40 CFR §230.3(s)(3). The agencies likewise gave an expansive interpretation of wetlands adjacent to those waters, defining “adjacent” to mean “bordering, contiguous, or neighboring.” §203.3(b). In United States v. Riverside Bayview Homes, Inc., 474 U. S. 121, the Court confronted the Corps’ assertion of authority under the CWA over wetlands that “actually abut[ted] on a navigable waterway.” Id., at 135. Although concerned that the wetlands fell outside “traditional notions of ‘waters,’ ” the Court deferred to the Corps, reasoning that “the transition from water to solid ground is not necessarily or even typically an abrupt one.” Id., 132–133. Following Riverside Bayview, the agencies issued the “migratory bird rule,” extending CWA jurisdiction to any waters or wetlands that “are or would be used as [a] habitat” by migratory birds or endangered species. 53 Fed. Reg. 20765. The Court rejected the rule after the Corps sought to apply it to several isolated ponds located wholly within the State of Illinois, holding that the CWA does not “exten[d] to ponds that are not adjacent to open water.” Solid Waste Agency of Northern Cook Cty. v. Army Corps of Engineers, 531 U. S. 159, 168 (SWANCC) (emphasis deleted). The agencies responded by instructing their field agents to determine the scope of the CWA’s jurisdiction on a case-by-case basis. Within a few years, the agencies had “interpreted their jurisdiction over ‘the waters of the United States’ to cover 270-to-300 million acres” of wetlands and “virtually any parcel of land containing a channel or conduit … through which rainwater or drainage may occasionally or intermittently flow.” Rapanos, 547 U. S., at 722 (plurality opinion).
