The Neosho River is a tributary of the Arkansas River in eastern Kansas and northeastern Oklahoma in the United States. Its tributaries also drain portions of Missouri and Arkansas. The river is about 463 miles (745 km) long. Via the Arkansas, it is part of the Mississippi River watershed. Its name is an Osage word meaning "clear water." The lower section is also known as the Grand River.

The Arkansas River is a major tributary of the Mississippi River. It generally flows to the east and southeast as it traverses the U.S. states of Colorado, Kansas, Oklahoma, and Arkansas. The river's source basin lies in Colorado, specifically the Arkansas River Valley. The headwaters derive from the snowpack in the Sawatch and Mosquito mountain ranges. It flows east into Kansas and finally through Oklahoma and Arkansas, where it meets the Mississippi River.