River Flow, Locks, Dams and Levees

Why It Is Important

The Mississippi River basin is the third largest watershed in the world, after the Amazon and Congo basins, respectively. Through its vast tributary system, the basin reaches from the northern Rocky Mountains in the west to the Appalachian Mountains in the east. The system drains parts, or all, of 31 states and two Canadian provinces across a landscape of 1.2 million square miles, comprising 41% of the contiguous United States and 15% of the North American continent. The Mississippi River flows into its delta and the Gulf of Mexico at the average rate of 811,530 cubic feet per second— the third largest river basin in the world.¹

The Mississippi River watershed is comprised of six distinct basins: the Upper Mississippi, Ohio River, Missouri River, Tennessee River, Arkansas Red and White Rivers and the Lower Mississippi.

Human Intervention

Before human intervention, the Mississippi River flowed through the landscape in a changing mix of main channels and side channels, splitting and rejoining around hundreds of islands, periodically flooding its surrounding lowlands or floodplains. This pattern produced a wide range of habitats within and around the river, from swampy backwaters to oxygen-rich rapids and from island chains to fertile plains enriched with the sediments deposited from floods.

Humans used the Mississippi River corridor for transportation and trade for thousands of years without changing its natural flow. But as the American frontier expanded westward, the River’s natural hazards to navigation were met with engineering prowess, creating channels which were safer for large vessels to transport both passengers and commodities. To achieve this greater flow of people and products, the Army Corps of Engineers constructed a series of 26 locks and dams between Minneapolis and St. Louis, fundamentally changing the River's natural flow and habitat.

While the River has been modified to allow for increased traffic, a separate engineering effort has existed to control the River's floods. Over the years, levees have been constructed in various communities from Commerce, MO, to New Orleans, limiting floods in these communities in most years, but also changing the River’s natural flow and distribution of sediments, converting important riverside habitats and floodplains into man-made embankments. Nutrients that previously enriched floodplain soils and sediments that built coastal wetlands are now blocked and channeled into the Gulf of Mexico instead.

Today's Mississippi is a highly-engineered system. All the structural changes have contributed to rapid loss of coastal wetlands and other natural habitat. They have also degraded water quality in the River and the Gulf and have shifted, and sometimes intensified, patterns of flooding and erosion.

What You Can Do

You can help restore and protect the River's natural state by volunteering with one of the many Mississippi River Network member organizations throughout the region. Please check out our map to find the one nearest you.

¹ National Research Council. (2008). Mississippi River Water Quality and the Clean Water Act.  The National Academies Press: Washington, DC.