Grand River. 1 River, 260 mi (418 km) long, rising in S Mich. and flowing N to Lansing, then NW to Lake Michigan at Grand Haven. It is the longest river in the state and is navigable to the city of Grand Rapids, which grew there because of the availability of waterpower. 2 River, rising in SW N.Dak. and flowing 209 mi (336 km) SE through S.Dak. to the Missouri River near Mobridge. Shadehill Dam (1951), located on the river, was built for flood control and irrigation as part of the Missouri River basin project. 3 River in Okla.: see Neosho, river; Pensacola Dam.