2. The Missouri River is the longest tributary of the Mississippi River, flowing for over 2,500 miles from its source in the Rocky Mountains in Montana to its confluence with the Mississippi River near St. Louis, Missouri. The Missouri River Basin drains an area of over 500,000 square miles, encompassing 10 states and two Canadian provinces. The Missouri River is a vital transportation route and a source of water for drinking, irrigation, and industry.
3. The Ohio River is the largest tributary of the Mississippi River, flowing for over 981 miles from its source at the confluence of the Allegheny and Monongahela rivers in Pittsburgh, Pennsylvania, to its confluence with the Mississippi River near Cairo, Illinois. The Ohio River Basin drains an area of over 200,000 square miles, encompassing 14 states. The Ohio River is a vital transportation route and a source of water for drinking, irrigation, and industry.