The Little Sioux River is a river in the United States. It rises in southwestern Minnesota near the Iowa border and continues to flow southwest for 258 miles (415 km) across northwest Iowa into the Missouri River at Little Sioux. The Little Sioux River was known as Eaneah-waudepon or "Stone River" to the Sioux Indians. Its tributaries include the Ocheyedan River, Maple River and the West Fork of the Little Sioux River. The Little Sioux River is integral to the Nepper Watershed Project, a major Iowa flood control and soil conservation program that was introduced in 1947. At Turin, Iowa, the Little Sioux River has a mean annual discharge of 1,761 cubic feet per second.