Overview:A community portal about The Mississippi River with blogs, videos, and photos. According to Wikipedia.org: The Mississippi River, derived from the old Ojibwe word misi-ziibi meaning'great river', is the second-longest river in the United States ; the longest is the Missouri River, which flows into the Mississippi. Taken together, they form the largest river system in North America. If measured from the head of the Missouri, the length of the Missouri-Mississippi combination is approximately 3900 miles, making the combination the 4th longest river in the world. Apart from the Missouri, the largest of the many large Mississippi tributaries is the Ohio River. The Mississippi River is the main river that supports much of the American civilization.