The Atchafalaya Basin is the nation's largest river swamp, containing almost one million acres of America's most significant bottomland hardwoods, swamps, bayous, and backwater lakes.

The basin begins near Simmesport, La., and stretches 140 miles southward to the Gulf of Mexico. Currently, the Atchafalaya Basin is bound by natural ridges formed by levee building along active and abandoned courses of the Mississippi River.

Estimates show that close to 22 million pounds of crawfish is commercially harvested annually from the basin.

Over the past 10,000 years or more, the Mississippi River has changed its path several times, ranging from the current location of Bayou Teche to today's route past Baton Rouge and New Orleans. The Atchafalaya River runs down the middle of that traditional Mississippi floodplain and would probably be the main channel of the Mississippi by now, if not for the Old River Control Structure[s] near Simmesport.

Formerly the lower section of the Red River, the Atchafalaya River became much smaller after the Red joined the Mississippi in the 15th century. By the 19th century, the Atchafalaya was blocked by a huge log raft, as were parts of the Red.