When geographers measure rivers, the length includes what are known as “stems”. These are the largest downstream portions of a river. Merriam Webster defines these as “the main course of a river of stream”. These even have a designation. Called the Strahler system, it measured rivers by their stems. On a scale of zero to 10, the only river in America that rates a 10 is the Mississippi.
There are only 38 rivers in America that run over 500 miles based on the Strahler system. Nearly all are in the West. Each terminates in what is known as the river’s “mouth”. For example, the Mississippi’s mouth is where it enters the Gulf of Mexico.
The longest river in America is the Missouri River, which is 2,341 miles long. This is barely longer than the Mississippi which is 2,340 miles long. The Missouri River starts in the Rocky Mountains and runs until it empties into the Mississippi in St. Louis.
Americans used the Missouri to travel West, particularly into the Plains states. The river runs through parts of Montana, South Dakota, North Dakota, Nebraska, Missouri, Kansas, and Iowa.
According to Britannica, “The river’s drainage basin occupies about 529,400 square miles (1,371,100 square km) of the Great Plains, of which 2,550 square miles (16,840 square km) are in southern Canada.”
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