St Louis marks a dividing line in the Mississippi River. To the north, in Minnesota, it is a national treasure attracting more people for recreation than Yellowstone National Park. To the south, it is hardly a river anymore. It more closely resembles a drainage pipe.

As it journeys through the middle of America, the Mississippi suffers the bombardments of human civilization, deteriorating with each mile. Several factors contribute to its degradation. For one, the river becomes more and more polluted with run-off from the whopping 40 percent of US land that it drains: chemical fertilizers from agriculture, industrial toxins, as well as sewage and waste. By the time it reaches Louisiana, the water is so filthy that the government advises against eating the fish or swimming in the river.

But there is another reason why the Mississippi today is like two different rivers. At the northern reaches, it still flows virtually untamed, as it has since glaciers first formed it hundreds of thousands of years ago. Along the way, however, it becomes increasingly constrained by locks, dams, and levees constructed both to create agricultural land and to ensure a minimum nine foot-deep navigation channel for the barges that swim constantly back and forth with their cargo. In St Louis, the great river is 50 percent severed from its natural floodplains. South of St Louis, less than ten percent of the Mississippi River flows free.
Why does it matter?

John Chick, Field Station Director for the National Great Rivers Research and Education Center and the Illinois Natural History Survey, explains why. Standing on a hillside in Illinois overlooking a mile-wide swath of the brown, fast-flowing Mississippi, he says, “The river is much more than what you see here, the water stretching from this bank to that bank. It naturally would cover a broad area of land far out on either side that would seasonally flood due to rainfall and snowmelt. All the organisms in the river are designed to take advantage of that. Plants grow in the backwater lakes, then fish move in to get food, reproduce, and rear their offspring.”

“So what happens when the river is cut off from its floodplains?” I ask.

John replies, “When you levee the floodplain from a river, you’re leveeing off 90 percent of the ecosystem, because the floodplain is huge relative to the river’s size.

“Water isn’t allowed to flow back and forth from the wetlands into the river. An excess of sediments builds up in backwater areas, which makes the water so cloudy that sunlight can’t penetrate. As a result, plants can’t grow, fish can’t reproduce, and wildlife can’t feed. The habitat is completely destroyed.

“In addition, the water flowing into the floodplains would deposit nutrients on the soil, making it more fertile. Now that natural process isn’t occurring, farmers use chemical fertilizers to make their land more productive instead.”

John concludes, “This flood pulse—the annual rise and fall of water levels that naturally occurs along all rivers—is the heartbeat of the Mississippi. It drives the ecosystem. Along the lower Mississippi, we’ve virtually stopped that heart from beating.”