Outline Map of the USA With Major Rivers Shows that the Country has over 250,000 rivers. The longest river in the USA is the Missouri River. it is a tributary of the Mississippi River and is 2,540 miles long. But the biggest in terms of water volume is the deeper Mississippi River.
According to Map of the USA With Major Rivers, Seven Major Rivers of USA cross or form international boundaries. The Yukon and Columbia rivers that begin in Canada and flow into the United States. The Milk and Saint Lawrence rivers and the Red River of the North begin in the US and flow into Canada.
Of these, only the Milk River crosses the international border twice, leaving and then re-entering the United States. Colorado and the Rio Grande river begin in the United States and flow into or from a border with Mexico. The Missouri River is the longest river in the United States at 2,540 miles long. Together with the Mississippi River, it forms the fourth largest river system in the world.