Little Sioux (sō) [key], river, 221 mi (356 km) long, rising in SW Minn. and flowing generally SW across NW Iowa to the Missouri River S of Sioux City. Flowing through a rich agricultural area in the Corn Belt, the river is used extensively for irrigation. The Nepper watershed project, near Mapleton, Iowa, consisting of four dams, was completed in 1948. Serious floods in 1953 and 1954 led to programs for flood control and soil conservation.
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