Animals that need less oxygen, such as catfish, do well in still waters. Hundreds of millions of migrating birds fly the entire Mississippi, from the chilly North to the subtropical South, from rapids to still waters. Plus, otters, beavers, and other land animals live on the banks. Count humans among them. Since prehistoric times, boats have carried people and goods up and down the Mississippi.
People change the river's biomes more dramatically than any other residents.
They build homes, factories, and resorts right on the riverbanks. They dam the river to create deep water so the river can be used for commercial navigation. They pollute the water with chemicals such as fertilizer. In spite of levees, however, bad floods still happen. In 1993, the Mississippi flooded, killing dozens of people and leaving 62,000 families homeless.