Perdido River, historically Rio Perdido (1763), is a river in the U.S. states of Alabama and Florida; the Perdido, a designated Outstanding Florida Waters river, forms part of the boundary between the two states along nearly its entire length and drains into the Gulf of Mexico. During the early 19th century it played a central role in a series of rotating boundary changes and disputes among France, Spain, Great Britain, and the United States. It rises in southwestern Alabama in Escambia County approximately northwest of Atmore. It flows south approximately to latitude 31°N, south of which it forms the remainder of the Alabama/Florida border. It flows generally east-southeast in a winding course and enters the north end of Perdido Bay on the Gulf of Mexico, approximately west of Pensacola. The word "perdido" is Spanish for "lost". History From 1682 to 1763, the Perdido formed the boundary between the French colony of Louisiana and the Spanish colony of Florida. Following the British victory over the French in the French and Indian War, Great Britain received the French colonial territory between the Mississippi River and the Perdido River, as well as the Spanish colony of Florida, while Spain received the formerly French territory west of the Mississippi, plus the city of New Orleans. The British divided their newly acquired colony into West Florida and East Florida at the Apalachicola River (whose main tributary, the Chattahoochee River, forms a large portion of the present boundary between Alabama and Georgia, and a small part of the Florida/Georgia boundary). Twenty years later, as part of the Treaty of Paris, Britain returned all of Florida to Spain, at which point Spain controlled the entire coast of the Gulf of Mexico. (Spain maintained the West and East Florida colonial designations that the British had established.) In 1800, as part of the Treaty of San Ildefonso, Spain returned the Louisiana colony to France, retaining control of the lands east of the Mississippi River (except New Orleans). In 1803, France sold Louisiana (New France) to the United States in the Louisiana Purchase. A boundary dispute erupted between the U.S. and Spain, with the U.S. claiming the land west of the Perdido River as part of the original Louisiana (New France) colony, whereas the Spanish claimed that only the portion of Louisiana west of the Mississippi River had been returned to France. The Gulf coast south of 31 degrees latitude,