 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 consists primarily of <unk> , willows and <unk> , with several other types of trees such as maple and ash . Average tree height generally increases 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 does not support many aquatic invertebrates . However , the basin does support about 300 species of birds and 150 species of fish , some of which are endangered such as the <unk> <unk> . The Missouri 's aquatic and riparian habitats also support several species of mammals , such as <unk> , river otters , <unk> , <unk> , and raccoons . 
