The Missouri River is the longest river in North America, stretching over 2, 300 miles. It is formed by the confluence of the Osage, Platte, and SAC rivers. The Osage River is a tributary of the Missouri River that flows through central Missouri and is about 550 miles long. The Platte River is a tributary of the Missouri River that flows through Nebraska and is about 310 miles long. The SAC River is a tributary of the Missouri River that flows through southwestern Missouri and is about 200 miles long.