A bayou (pronounced or [ˈbaɪ uː]) is a small, slow-moving stream or creek formed in the former bed of a river. Bayous are usually located in low-lying areas, especially in the Mississippi River delta region of the southern United States. Many bayous are the home of crawfish, certain species of shrimp, other shellfish and catfish.

The word was first used by the French in Louisiana and is thought to originate from the Choctaw word bayuk which means "small stream". The first settlements of Acadians in southern Louisiana were near Bayou Lafourche and Bayou des Ecores which led to a close association of the bayou with Cajun culture.

A term used in the western US for generally similar features is "slough" (pronounced "slew"). Houston, Texas is known as the "Bayou City".

Bayou Country is most closely associated with Cajun (Acadian French) and Creole (mixed French, African, and Indian) cultural groups native to the Gulf Coast region generally stretching from Houston, Texas to Mobile, Alabama with its center in New Orleans, Louisiana.

See also wetland