The Missouri River is the longest river in North America and flows from the semi-arid western states to the relatively moist Midwest. An integrated system of large reservoirs, constructed in the mid-20th century, provides important water storage, hydroelectricity and flood control benefits. This system has been managed by the US Army Corps of Engineers which has traditionally followed its original mandate to support navigation and flood control. As water uses and societal values have evolved, the management of the river has slowly evolved, and the Army Corps of Engineers has adopted adaptive management to incorporate biological uncertainties into its decision-making. Other evolution, including the incorporation of economic incentives into water management, has failed to occur.