After U.S. Supreme Court decisions in SWANCC and Rapanos, the scope of "waters of the U.S." protected under all Clean Water Act (CWA) programs has been an issue of considerable debate and uncertainty. The Act has a single definition for "waters of the United States." As a result, these decisions affect the geographic scope of all CWA programs. SWANCC and Rapanos did not invalidate the current regulatory definition of "waters of the United States." However, the decisions established important considerations for how those regulations should be interpreted, and experience implementing the regulations has identified several areas that could benefit from additional clarification through rulemaking. The U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers proposed a rule for determining whether a water is protected by the Clean Water Act. This rule will make clear which waterbodies are protected under the CWA.