 Since the beginning of river commerce and industrial development in the 1800s , the Missouri has been severely polluted and its water quality degraded by human activity . Most of the river 's floodplain habitat is long gone , replaced by irrigated agricultural land . Development of the floodplain has led to increasing amounts of people and infrastructure within areas at high risk of inundation . <unk> have been constructed along more than a third of the river in order to keep <unk> within the channel , but with the consequences of faster stream velocity and a resulting increase of peak flows in downstream areas . <unk> runoff , which causes elevated levels of nitrogen and other nutrients , is a major problem along the Missouri River , especially in Iowa and Missouri . This form of pollution also heavily affects the upper Mississippi , Illinois and Ohio Rivers . Low oxygen levels in rivers and the vast Gulf of Mexico dead zone at the end of the Mississippi Delta are both results of high nutrient concentrations in the Missouri and other tributaries of the Mississippi . 
