 During the 20th century , the Missouri River basin was extensively developed for irrigation , flood control and the generation of hydroelectric power . Fifteen dams <unk> the main stem of the river , with hundreds more on tributaries . <unk> have been cut and the river <unk> to improve navigation , reducing its length by almost 200 miles ( 320 km ) from pre @-@ development times . Although the lower Missouri valley is now a populous and highly productive agricultural and industrial region , heavy development has taken its toll on wildlife and fish populations as well as water quality . 
