While it has been years in the making, the U.S. Army Corps of Engineers and the U.S. Environmental Protection Agency today published the final rule clarifying the agencies’ interpretation of the term “Waters of the United States” and the overall jurisdictional reach of the Clean Water Act. The rule is effective on August 28, 2015. According to the agencies their “interpretation is based not only on legal precedent and the best available peer-reviewed science, but also on the agencies' technical expertise and extensive experience in implementing the CWA over the past four decades.” The rule, moreover, “does not affect any of the exemptions from CWA section 404 permitting requirements provided by CWA section 404(f), including those for normal farming, ranching, and silviculture activities” and “expands regulatory exclusions from the definition of ‘waters of the United States’ to make it clear that this rule does not add any additional permitting requirements on agriculture.” In a modification from the proposed rule, the final rule “does not regulate shallow subsurface connections nor any type of groundwater[.]” Nevertheless, the agencies have determined that certain waters are categorically included within the CWA’s jurisdictional reach. Four types of waters, traditional navigable waters, interstate waters, impoundments of jurisdictional waters, and the territorial seas, are jurisdictional by rule in all cases. Two types of waters, “tributaries” and “adjacent” waters, for the first time are jurisdictional by rule, as defined, “because the science confirms” their significant nexus to other jurisdictional waters. For waters that are jurisdictional by rule, no additional analysis is required. All other jurisdictional waters are those found after a case-specific analysis to have a significant nexus to other jurisdictional waters, “either alone or in combination with similarly situated waters in the region.” This latter point, aggregation of waters for purposes of making jurisdictional determinations, has been hotly debated. The regulation will be fully subject to judicial review on July 13, 2015. The finality of the rule is almost certain to set off a slew of lawsuits challenging its validity and conformance with prior Supreme Court decisions.