The James River (also known as the Jim River or the Dakota River) is a tributary of the Missouri River, approximately 710 mi (1,143 km) long, in the U.S. states of North Dakota and South Dakota. The river provides the main drainage of the flat lowland area of the Dakotas between the two plateau regions known as the Coteau du Missouri and the Coteau des Prairies. This narrow area was formed by the lobe of a glacier during the last ice age, and as a consequence the watershed of the river is slender and it has few major tributaries for a river of its length. The James River has the somewhat dubious distinction of being the longest unnavigable river in the world.