The Cottonwood River is a tributary of the Minnesota River, 152 miles long, in southwestern Minnesota in the United States. Via the Minnesota River, it is part of the watershed of the Mississippi River, draining an area of 1,313 square miles in an agricultural region. The river's name is a translation of the Dakota name for the river, Wáǧa Ožú Wakpá, for th…The Cottonwood River is a tributary of the Minnesota River, 152 miles long, in southwestern Minnesota in the United States. Via the Minnesota River, it is part of the watershed of the Mississippi River, draining an area of 1,313 square miles in an agricultural region. The river's name is a translation of the Dakota name for the river, Wáǧa Ožú Wakpá, for the cottonwood tree groves, which are common along prairie rivers. It has also been known historically as the Big Cottonwood River.