 The Upper Missouri River is north of Gavins Point Dam the last hydroelectric dam of 15 on the river and it 's just upstream from Sioux City , Iowa . The lower Missouri River is the 840 river miles until it meets the Mississippi just above St. Louis . The Lower Missouri River has no <unk> or Lock and dams but it has a <unk> of Wing dams that enable barge traffic by directing the flow of the river into a 200 foot wide , 12 foot deep channel . These wing dams have been put in place and maintained by the U.S. Army corps of engineers , and there currently are no plans to construct any Lock and dams to replace these wing dams on the Missouri River . 
