The Niobrara River (/ˌnaɪ.əˈbrærə/; from the Ponca Ní Ubthátha khe pronounced [nĩꜜ ubɫᶞaꜜɫᶞa kʰe], meaning "water spread-out horizontal-the") is a tributary of the Missouri River, approximately 568 miles (914 km) long, running through the U.S. states of Wyoming and Nebraska. The river drains one of the most arid sections of the Great Plains, and has a low flow for a river of its length.