AbstractThe question of the kinds of water bodies federal and state agencies may regulate under the federal Clean Water Act (CWA) has reached the US Supreme Court 3 times without clear resolution. The Waters of the United States (WOTUS) rule adopted by the Environmental Protection Agency and the Army Corps of Engineers (collectively, the agencies), based in part on a recent synthesis of science regarding the connectivity of surface waters (USEPA 2015), seeks to reduce regulatory uncertainty by clarifying which waters are subject to CWA regulation. The rule makes progress in that regard, but has been challenged in court on grounds that the agencies seek jurisdiction over waters that are not properly covered in the CWA, and members of Congress have taken steps to overturn the rule legislatively. The rule’s legality depends on: 1) the breadth of federal constitutional authority over “navigable” waters, 2) the text and meaning of the CWA, and 3) the relationship between the proposed regulation and the science...