Old River Control Structure, Water control facility in central Louisiana, United States.

The Old River Control Structure is a floodgate complex on the west bank of the Mississippi at River Mile 315, where the Atchafalaya River branches off. It holds four structures on the site of the former Upper Old River: the Low Sill Control Structure, the Overbank Structure, the Auxiliary Structure and the Sidney A. Murray Jr. Hydroelectric Station. A navigation lock stands separately to the south on the Lower Old River. Louisiana Highway 15 crosses the complex.

The installation was built between 1954 and 1963 after engineers realized the Mississippi wanted to shift its main course. The Corps of Engineers carried out the work to keep the river in its present bed and protect the coastal region from an uncontrolled shift.

The name Old River comes from the former channel of the Mississippi left after Captain Henry M. Shreve cut through Turnbull's Bend in 1831. Louisiana Highway 15 crosses the complex, passing the power plant, the Overbank Structure, the Low Sill structure, the auxiliary structure and the Old River Lock. The lock lets barges and ships pass between the Mississippi and the Atchafalaya and Red rivers.

The site sits away from larger towns and is reached by secondary roads that run along the riverbank. Visitors should note that access is limited since this is an active facility monitored around the clock.

Without this installation the Mississippi would shift its course entirely within decades and leave large parts of Louisiana dry. The facility forces the river to flow against its natural tendency and prevents one of the largest geographic changes in North American history.