The Atchafalaya Basin, or Atchafalaya Swamp, is the largest wetland and swamp in the United States. Located in south central Louisiana, it is a combination of wetlands and river delta area where the Atchafalaya River and the Gulf of Mexico converge. The river stretches from near Simmesport in the north through parts of eight parishes to the Morgan City area in the south. The Atchafalaya is unique among Louisiana basins because it has a growing delta system with nearly stable wetlands. The basin contains about 70% forest habitat and about 30% marsh and open water. It contains the largest contiguous block of forested wetlands remaining in the lower Mississippi River valley and the largest block of floodplain forest in the United States. Best known for its iconic cypress-tupelo swamps, at 260,000 acres, this block of forest represents the largest remaining contiguous tract of coastal cypress in the US.

The Atchafalaya Basin Bridge, also known as the Louisiana Airborne Memorial Bridge, is a pair of parallel bridges in the U.S. state of Louisiana between Baton Rouge and Lafayette which carries Interstate 10 over the Atchafalaya Basin. With a total length of 96,095 feet or 18.2 miles, it is the second-longest bridge in the US and fourteenth-longest in the world by total length.