The Tombigbee River is a tributary of the Mobile River, approximately 400 mi (644 km) long, in the U.S. states of Mississippi an Alabama. It is one of two major rivers, along with the Alabama River, that unite to form the short Mobile River before it empties into Mobile Bay on the Gulf of Mexico. The Tombigbee watershed encompasses much of the rural coastal plain of western Alabama and northeastern Mississippi, flowing generally southward. The river provides one of the principal routes of commercial navigation in the southern United States, navigable along much of its length through locks and connected in its upper reaches to the Tennessee River via the Tennessee-Tombigbee Waterway. Pleasure boats cruising America's Great loop use the waterway each year in the fall.