Red River, a major river in the southern United States. It begins on the high plains of eastern New Mexico and flows 1,222 miles (1,967 km) southeastward through Texas, Oklahoma, Arkansas, and Louisiana, where the river flows into two distributaries, the Atchafalaya River, which empties into the Gulf of Mexico, and the Old River, which flows to the Mississippi River. Regulation of the river is part of a flood-control project on the lower Mississippi.
Tributaries of the Red include the Black-Ouachita and Washita rivers. The Red River's name comes from the red color of the water, resulting from the red clay in much of the river's valley.
When Europeans explored the river in the early 1700's, they found great masses of logs and brush blocking the channel in what is now northern Louisiana and southwestern Arkansas. Navigation was long hindered until the Great Raft, as the entire obstruction was called, was finally cleared in the 1830's. For a time the Red was an important steamer route, but it declined as the railways came into prominence. On the Red and its tributaries are a number of flood-control and hydroelectric projects. Denison Dam, on the Texas-Oklahoma border, impounds Lake Texoma, the largest reservoir on the river.