Historically , the thousands of square miles that comprised the floodplain of the Missouri River supported a wide range of plant and animal species . Biodiversity generally increased proceeding downstream from the cold , subalpine headwaters in Montana to the temperate , moist climate of Missouri . Today , the river 's riparian zone consist primarily of cottonwoods , willows and sycamores , with several other types of trees such as maple and ash . Average tree height generally increase farther from the riverbanks for a limited distance , as land adjacent to the river is vulnerable to soil erosion during floods . Because of its large sediment concentrations , the Missouri do not support many aquatic invertebrates . However , the basin do support about 300 species of birds and 150 species of fish , some of which are endangered such as the pallid sturgeon . The Missouri 's aquatic and riparian habitats also support several species of mammals , such as minks , river otters , beavers , muskrats , and raccoons .