The Sixth Circuit recently struck down an EPA Clean Water Act (CWA) regulation that sought to define reasonable boundaries of the National Pollutant Discharge Elimination System (NPDES) permitting program in the context of pesticide use.1 For CWA practitioners, the decision is signifi cant for its sweeping expansion of the definition of regulated “point source” discharges and the resulting implications for a wide range of activities now subject to the threat of CWA enforcement. But it is also noteworthy for followers of administrative law generally, because of the court’s invalidation of an EPA regulation and 35 years of consistent agency practice based on what may reasonably be characterized as conclusory assertions of the statute’s “plain” meaning, rather than faithful adherence to the traditional Chevron analysis...