The Missouri River Basin is a large watershed in the United States, primarily draining the states of Montana, North Dakota, South Dakota, Nebraska, Kansas, Iowa, Missouri, and Wyoming. It covers an area of about 529,000 square miles, making it the largest river basin in North America. The basin is home to the Missouri River, which is the longest river in the U.S., flowing approximately 2,341 miles before joining the Mississippi River. The basin plays a crucial role in the region's ecology and economy. It supports diverse wildlife and provides water for agriculture, industry, and urban areas. Major cities within the basin include Kansas City and St. Louis. The basin also features several reservoirs and dams, such as the Gavins Point Dam, which help manage water flow and provide recreational opportunities.