Big Sioux River
（重定向自Big Sioux）
![The falls of the Big Sioux River at Sioux Falls, South Dakota](/Images/godic/202412/24/Sioux_Falls-waterfall0411.jpeg")
![The course and watershed of the Big Sioux River.](/Images/godic/202412/24/BigSiouxCourseWatershed10412.png")
![This excerpt from the Lewis and Clark map of 1814 shows the rivers of western Iowa and eastern South Dakota. The Big Sioux River (](/Images/godic/202412/24/Lewis_and_Clark_Middle_Missouri_BigSioux_James0412.jpg")
![](/Images/godic/202412/24/Sioux_falls_sd_falls_park0412.jpg")
The Big Sioux River is a tributary of the Missouri River, 419 miles (674 km) long, in eastern South Dakota and northwestern Iowa in the United States. The United States Board on Geographic Names settled on "Big Sioux River" as the stream's name in 1931. The river was named after the Lakota people (Sioux Indians).