Speaking very generally and off the cuff, the river is open to barge traffic from Sioux City, IA to the mouth of the river in St. Louis. From Sioux City to Gavins Point Dam in South Dakota, it's much like the Missouri of old -- muddy, islands, sandbars, etc. Upstream, there are three more impassible dams in South Dakota and one each in North Dakota and Montana. Above Fort Peck Dam in Montana, I'm not sure how far it remains navigable. Anyone from Montana who could chime in?