Red River

The Red River is a major river in the Southern United States. It was named for its reddish water color from passing through red-bed country in its watershed. It is known as the Red River of the South to distinguish it from the Red River of the North, which flows between Minnesota and North Dakota into the Canadian province of Manitoba. Although once a tributary of the Mississippi River, the Red River now is a tributary of the Atchafalaya River, a distributary of the Mississippi that flows separately into the Gulf of Mexico. This confluence is connected to the Mississippi River by the Old River Control Structure.

The south bank of the Red River formed part of the US–Mexico border from the Adams–Onís Treaty (in force only in 1821) until the Texas Annexation and the Treaty of Guadalupe Hidalgo.