Arkansas River

The Arkansas River is a major tributary of the Mississippi River. A tributary is a smaller river that flows into a larger one. This river flows east and southeast across the United States. It travels through the states of Colorado, Kansas, Oklahoma, and Arkansas. It is a very significant waterway in North America. The river is the sixth-longest river in the United States. It is also the second-longest tributary in the Mississippi–Missouri system. Globally, it ranks as the 47th longest river.

The river begins in the Rocky Mountains within the Arkansas River Valley. Its headwaters come from the snowpack in the Sawatch and Mosquito mountain ranges. Specifically, the origin is located in Lake County, Colorado, near Leadville. The river's path changes through three distinct physical sections. In the first section, it is a steep, fast-flowing mountain river. This part of the river drops significantly in elevation. It moves through narrow valleys in the Rockies. This section is popular for whitewater rafting in areas like Brown's Canyon and the Royal Gorge.

As the river moves, its character changes again. At Cañon City, Colorado, the valley widens and flattens. West of Pueblo, Colorado, the river enters the Great Plains. In this middle section, the river is a typical Great Plains waterway. It has wide, shallow banks. It is subject to seasonal flooding and periods of very low flow. Many tributaries, such as the Cimarron and Salt Fork Arkansas rivers, join the main channel.

The third section occurs as the river moves through Oklahoma and Arkansas. In eastern Oklahoma, the channel becomes more consistent and contained. To maintain reliable flow rates, engineers built many dams and large reservoir lakes. These structures sit on the Arkansas and its intersecting tributaries. These tributaries include the Canadian, Verdigris, Neosho, Illinois, and Poteau rivers. These dams allow the river to be navigable for large barges. The McClellan-Kerr Arkansas River Navigation System joins the Verdigris River to help move goods.

History shows that the river's path has shifted over thousands of years. Sediments found in a palaeochannel near Nolan show the river meandered through that area by 3200 BCE. A meander belt is the area where a river curves and shifts its path. Scientists found this channel was inactive 400 years before a nearby Mississippi River channel became active. Human history is also tied to the water. Many Native American nations lived along the 1,450-mile stretch for thousands of years. In 1859, placer gold was discovered near Leadville. This discovery brought thousands of people to the area to seek wealth.

European explorers also documented the river. The Spanish Coronado expedition saw the river in 1541. They originally called it Napeste. Later, the French explorer Jacques Marquette called it Akansa in 1673. He named it after the tribal people living there, known today as the Quapaw. French traders also used dugout canoes called pirogues. They made these by hollowing out large cottonwood trees. These trees were plentiful along the southern rivers.

Managing the river involves complex legal and environmental systems. Because the river crosses many state lines, water rights are often disputed. Since 1902, Kansas has sued Colorado over how much water is taken. These disputes have reached the U.S. Supreme Court. To manage this, the Arkansas River Compact was approved by Congress in 1949. Later, the Kansas–Oklahoma Arkansas River Basin Compact was created in 1965. These agreements help promote equity in water use. Additionally, water flow in central Kansas has dropped recently. This is largely due to groundwater pumping for irrigation in Colorado and Kansas.