The World Wide Fund For Nature divide the Missouri River watershed into three freshwater ecoregions : the Upper Missouri , Lower Missouri and Central Prairie . The Upper Missouri , roughly encompassing the area within Montana , Wyoming , southern Alberta and Saskatchewan , and North Dakota , comprise mainly semiarid shrub @-@ steppe grasslands with sparse biodiversity because of Ice Age glaciations . There are no known endemic species within the region . Except for the headwaters in the Rockies , there is little precipitation in this part of the watershed . The Middle Missouri ecoregion , extending through Colorado , southwestern Minnesota , northern Kansas , Nebraska , and parts of Wyoming and Iowa , have greater rainfall and is characterized by temperate forests and grasslands . Plant life is more diverse in the Middle Missouri , which is also home to about twice as many animal species . Finally , the Central Prairie ecoregion is situated on the lower part of the Missouri , encompassing all or parts of Missouri , Kansas , Oklahoma and Arkansas . Despite large seasonal temperature fluctuations , this region have the greatest diversity of plants and animals of the three . Thirteen species of crayfish are endemic to the lower Missouri .