Mississippi–Missouri–Jefferson–Beaverhead–Red Rock–Hell Roaring is the longest river in North America at 6,275 kilometers (3,899 miles).

At 6,275km (3,899 miles), the Mississippi–Missouri–Jefferson–Beaverhead–Red Rock–Hell Roaring river system is the longest in North America, helmed by the two longest rivers in the United States, the Missouri river (3,768 km) and the Mississippi River (3,544 km).The Missouri River is the longest river in North America. Originating from the Rocky Mountains of western Montana, the Missouri flows east and south for 2,341 miles (3,767 km) before merging into the Mississippi River. The Mississippi River has its sources at Lake Itasca and Brower's Spring in Montana, and stretches for another 3,544km southwards before flowing out eventually to the Gulf of Mexico.

The drainage area of the river spans 2,980,000 square kilometers and discharges at a rate of 16,792m³. The deepest part of the Mississippi River is in New Orleans, where its depth could reach 200 feet (61m).