Atchafalaya Basin

About

The Old River Control Structure, built in 1963, maintains the flow split that keeps 30% of the Mississippi's water diverted into the Atchafalaya Basin — preventing the larger river from abandoning its current channel entirely. This controlled flood carries an average of 95,000 CFS through 140 miles of America's largest river swamp, from Simmesport south to the Gulf through St. Martin and Iberia parishes. The upper basin runs open swamp channels toward Henderson, where the waterway spreads into lake-like expanses beneath towering cypress groves. Below Henderson, the lower basin transitions through Morgan City toward Atchafalaya Bay, where freshwater gives way to tidal marshes. Designated as a National Heritage Area in 2006, the basin encompasses both National Wildlife Refuge lands and active oil field infrastructure. At optimal flows between 50,000 and 200,000 CFS, navigation requires local knowledge — channels shift, and what looks like open water may be three feet deep or thirty. Outfitters like Atchafalaya Basin Landing and Pack & Paddle provide guided access to sections that would otherwise require swamp boat experience to navigate safely.