For: Mississippi River (Ontario)

The Mississippi River is the second longest river in the United States, with a length of from its source in Lake Itasca in Minnesota to its mouth in the Gulf of Mexico. The longest river, a Mississippi tributary, is the Missouri River measuring .

The Mississippi River is part of the Jefferson-Missouri-Mississippi river system, which is the largest river system in North America and among the largest in the world: by length ( ), it is the fourth longest, and by its average discharge of 572,000 cu ft/s (16,200 m³/s), it is the tenth largest river.

The name Mississippi is derived from the Ojibwe word misi-ziibi ("Great River") or gichi-ziibi ("Big River") at its headwaters.

Geography

The Missouri River flows from the confluence of the Jefferson, Madison, and Gallatin to the Mississippi River. Taken together, the Jefferson, the Missouri, and the Mississippi form the longest river system in North America. If measured from the source of the Jefferson at Brower's Spring, to the Gulf of Mexico, the length of the Mississippi-Missouri-Jefferson combination is approximately , making the combination the 4th longest river in the world. The uppermost of this combined river are called the Jefferson, the lowest are part of the Mississippi, and the intervening are called the Missouri.

The Arkansas River is the second longest tributary of the Mississippi River. Measured by water volume, the largest of all Mississippi tributaries is the Ohio River.

The widest point of the Mississippi River is Lake Winnibigoshish, near Grand Rapids, Minnesota at over across. Also of note is Lake Onalaska, near La Crosse, Wisconsin, where the river is over wide (created by Lock and Dam No. 7) and Lake Pepin at more than two miles (3 km) wide. However, these areas are lakes or reservoirs rather than free flowing water. In areas where the Mississippi is a flowing river, it exceeds one mile (1.6 km) in width in several places in its lower course.

The Mississippi River runs through 10 states and was used to define portions of these states' borders. The middle of the riverbed at the time the borders were established was the line to define the borders between states. The river has since shifted, but the state borders of Wisconsin, Iowa, Illinois, Missouri, Kentucky, Arkansas, Tennessee, and Mississippi have not changed; they still follow the former bed of the Mississippi River as of their establishment.