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Rh This is the thrust of observations in decisions going all the way back to Riverside Bayview. In that case, we deferred to the Corps’ decision to regulate wetlands actually abutting a navigable waterway, but we recognized “the inherent difficulties of defining precise bounds to regulable waters.” 474 U. S., at 134; see also id., at 132 (noting that “the transition from water to solid ground is not necessarily or even typically an abrupt one” due to semi-aquatic features like shallows and swamps). In such a situation, we concluded, the Corps could reasonably determine that wetlands “adjoining bodies of water” were part of those waters. Id., at 135, and n. 9; see also SWANCC, 531 U. S., at 167 (recognizing that Riverside Bayview “held that the Corps had … jurisdiction over wetlands that actually abutted on a navigable waterway”).

In Rapanos, the plurality spelled out clearly when adjacent wetlands are part of covered waters. It explained that “waters” may fairly be read to include only those wetlands that are “as a practical matter indistinguishable from waters of the United States,” such that it is “difficult to determine where the ‘water’ ends and the ‘wetland’ begins.” 547 U. S., at 742, 755 (emphasis deleted). That occurs when wetlands have “a continuous surface connection to bodies that are ‘waters of the United States’ in their own right, so that there is no clear demarcation between ‘waters’ and wetlands.” Id., at 742; cf. 33 U. S. C. §2802(5) (defining “coastal waters” to include wetlands “having unimpaired connection with the open sea up to the head of tidal influence”). We agree with this formulation of when wetlands are part of “the waters of the United States.” We also acknowledge that temporary interruptions in surface connection may sometimes occur because of phenomena like low tides or dry spells.