The Nebraska River is composed of three main rivers: the Platte, Loup, and Niobrara. The Platte River is a tributary of the Missouri River, originating in Colorado and flowing through Nebraska and Wyoming. The Loup River is a tributary of the Platte River, originating in central Nebraska and flowing eastward. The Niobrara River is a tributary of the Missouri River, originating in Wyoming and flowing through Nebraska and South Dakota. All three rivers converge to form the Nebraska River, which flows into the Missouri River.