Platte, river, c.310 mi (500 km) long, formed by the confluence of the North Platte (680 mi/1,090 km long) and South Platte (430 m/690 km) rivers at North Platte, Neb. It flows generally E across S Nebraska to join the Missouri River at Plattsmouth, Neb. The river is too flood-prone in spring and too shallow and braided the rest of the year for navigation. Much of its water and the water of its tributaries is diverted for irrigation, municipal uses, and hydroelectric power production. The Platte valley was an important route to the West in the 19th cent.; the Mormon Trail followed the north bank, and the Oregon Trail followed the south bank.