The Mississippi rises at Lake Itasca, and joined to the Missouri it is the fourth longest river system in the world

Background

The Mississippi River is the second longest river in North America and flows from its source at Lake Itasca through the centre of the continental United States.
The Missouri River, a tributary of the Mississippi River, is about 100 miles longer than the Mississippi's own main stem.
Compared with other world rivers, the Mississippi-Missouri combination ranks fourth in length at 3,710 miles/5,970km, after the Nile at 4,160 miles/6,693km, the Amazon at 4,000 miles/6,436km and the Yangtze at 3,964 miles/6,378km.
At Lake Itasca the river is between 20 and 30 feet wide, the narrowest stretch for its entire length; the widest part is at Lake Winnibigoshish, where it is wider than 11 miles, and the widest navigable section is Lake Pepin.
The Mississippi watershed drains about 3.2 million square kilometers (1.2 million square miles), including all or parts of 31 states and two Canadian provinces, about 40% of the continental United States.
That watershed is the fourth largest in the world, extending from the Allegheny Mountains in the east to the Rocky Mountains in the west.
At least 260 species of fish, 25% of all fish species in North America, live in the Mississippi River, and sixty percent of all North American birds (326 species) use the Mississippi River Basin as their migratory flyway.
Barges and their tows move approximately 175 million tons of freight each year on the upper Mississippi through a system of 29 locks and dams.