 In the late 19th and early 20th centuries , a great number of dams were built along the course of the Missouri , transforming 35 percent of the river into a chain of reservoirs . River development was stimulated by a variety of factors , first by growing demand for electricity in the rural northwestern parts of the basin , and also by floods and droughts that plagued rapidly growing agricultural and urban areas along the lower Missouri River . Small , privately owned hydroelectric projects have existed since the 1890s , but the large flood @-@ control and storage dams that characterize the middle reaches of the river today were not constructed until the 1950s . 
