What river flows between Nebraska and Iowa?

Missouri River, longest tributary of the Mississippi River and second longest river in North America. It is formed by the confluence of the Jefferson, Madison, and Gallatin rivers in the Rocky Mountains area of southwestern Montana (Gallatin county), U.S., about 4,000 feet (1,200 metres) above sea level. The Missouri proper has a total course of 2,315 miles (3,726 km).

The Missouri first flows northward and northeastward (via Great Falls) through western Montana before turning eastward across the northern portion of the state. Shortly after entering western North Dakota, it begins to trend southeastward before continuing southward just south of Bismarck into northern and central South Dakota to Pierre, where it again begins to trend southeastward. Continuing through central and southern South Dakota, the river then forms a section of the South Dakota–Nebraska boundary, the Nebraska–Iowa boundary, the Nebraska–Missouri boundary, and the northern section of the Kansas–Missouri boundary. At Kansas City, Kansas, the river again turns to the east and, after flowing through Kansas City, Missouri, meanders eastward across west-central Missouri before heading southeastward again to Jefferson City. There it makes its final eastward turn, flowing until it joins the Mississippi River about 10 miles (16 km) north of St. Louis.