In the past two decades, the Supreme Court has significantly reduced the deference given to the “Jurisdictional Determinations” made by the Army Corps of Engineers under section 404 of the Clean Water Act. Previous to the Court’s holding in Solid Waste Agency of Northern Cook County v. United States Army Corps of Engineers, the Court had continuously upheld the Corps’ interpretation of section 404’s jurisdictional reach. From Solid Waste Agency onwards, however, the Court has continuously raised the level of scrutiny applied to the Corps’ jurisdictional rules under section 404. This Note explores how the Supreme Court’s scrutiny of the Corps’ Jurisdictional Determinations has evolved, starting with the Court’s relatively lax approach in United States. v. Riverside Bayview Homes and followed by the Court’s gradual heightening of scrutiny through Solid Waste Agency, Rapanos v. United States, and Hawkes v. Army Corps of Engineers. This Note then examines how the conservative thrust of this evolution, which limits the Corps’ regulatory authority, has undermined the environmental mission that Congress designed in the Clean Water Act.