Along with its major tributaries like the
Missouri River and
Ohio River, the Mississippi forms the largest river system in the United States and the most important in the world in terms of the commerce that it carries. Starting as a small, clear stream out of Lake Itasca in north-central
Minnesota, it flows southward until it reaches the
Gulf of Mexico. It forms part of the boundaries of 10 states. The largest cities along its course are the twin cities of
Minneapolis and
St Paul in Minnesota,
St Louis, Missouri, where it joins the
Missouri River and
New Orleans near its mouth.