The Arkansas River is a river in the United States. It flows southeast and is a tributary of the Mississippi River. It is about 1,469 miles (2,364 km) long. It is the sixth longest river in the United States.
The Arkansas begins in the state of Colorado. Then, it flows through the states of Kansas and Oklahoma. It flows into the Mississippi River in Arkansas, which is named for the river. Riverboats go up the Arkansas River as far as Oklahoma.