On January 23, 2020, the U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers released a prepublication version of a final rule redefining which waters are subject to federal jurisdiction under the Clean Water Act (2020 Rule). A hotly contested question since the 1970s, this administration first repealed the Obama administration’s attempt at resolving the question. With the 2020 Rule, the administration places the following waters under U.S. jurisdiction: territorial seas, traditionally navigable waters, perennial and intermittent streams and their tributaries, lakes, ponds, and impoundments of jurisdictional waters, and wetlands “adjacent” to jurisdictional waters. The 2020 Rule, however, adds some new conditions to establish jurisdiction: tributaries have to flow to a jurisdictional water “in a typical year”; there must be regular surface flow to a jurisdictional water, not through groundwater and not ephemeral; wetlands must “abut” a jurisdictional water. The 2020 Rule rejects the “significant nexus” test and jurisdiction over neighboring waters, positions embraced by the prior administration. Once published, like the repeal, the 2020 Rule will be challenged in federal court. See Sidley’s client alert, EPA and U.S. Army Corps of Engineers Issue a Prepublication Version of their Rule Redefining “Waters of the United States,” for more detail.