The Atchafalaya Basin is one of the world’s most extensive river-floodplain systems and an important floodway made up of the West Atchafalaya Floodway, the Morganza Floodway, and the Lower Atchafalaya Floodway, which help protect millions of Americans from flooding by directing water from the Mississippi River through the Basin to the Gulf of Mexico and regulating the combined flow of the Red and Mississippi rivers at the Old River Control Structure near Simmesport. In the Lower Atchafalaya Floodway, levees about 15 miles apart built in the 1930s, along with the straightening of the river, permanently changed the Basin inside and outside the floodway: the river’s main passage shifted to the man-made Whiskey Bay Pilot Channel, the former channel through Butte La Rose began silting in, historic segments were cut off or closed to force more water into the new channel, and navigation improved. The levees also raised flood heights inside the Basin, removed traditional drainage paths from nearby areas, and contributed to the permanent migration of residents from small communities such as Atchafalaya, which arose in the early 1900s to support the Southern Pacific Railroad bridge destroyed in the Flood of 1927. Low areas outside the levees also experienced more flooding as rainwater moved through a restricted path and land subsided without annual river sediment. By the 1970s, deltas in the floodway’s lakes were largely complete, and during the Mississippi River Flood of 1973 a new Atchafalaya Delta began emerging in Atchafalaya Bay and continues to grow. The 18-mile Interstate 10 bridge completed in the 1970s reconnected both sides of the Basin. Today the biodiverse wetland supports fishermen and hunters, draws recreation, contains the largest block of forested wetlands in the lower Mississippi River valley and the largest block of coastal cypress forest in the U.S., and provides habitat for more than 85 species of fish and almost 300 species of resident and migratory birds, while facing challenges from hydrology effects, sedimentation, invasive species, and resource extraction.