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The Missouri River reservoir system is a critical national resource that provides a variety of benefits, including navigation, flood control, irrigation, hydropower, municipal and industrial water supply, recreation, and fish and wildlife habitat. The U.S. Army Corps of Engineers (Corps) is responsible for operating the Missouri River system to serve these congressionally authorized purposes. Between 1933 and 1964, the Corps built six dams on the Missouri River to serve the water resource needs within the Missouri River basin. The resulting reservoirs form a series of lakes from Montana to the South Dakota-Nebraska border. The Corps manages the system of dams and reservoirs according to the water control plan presented in its Missouri River Mainstem Reservoir System Master Water Control Manual, which was first published in 1960 and most recently revised in 2006. The master manual provides water control criteria for the reservoir system for a spectrum of anticipated runoff conditions. Annual operating plans based on these criteria provide detailed reservoir regulation for each operating year. Four states, Iowa, Nebraska, Kansas, and Missouri, are adjacent to the Missouri River and are served by barge and other vessel traffic along the river. Two states, Iowa and Missouri, are served by navigation on both the Missouri River and the Mississippi River. Both private companies and the Corps have conducted navigation activities on the Missouri River to and/or from these states. Companies transport numerous commodities, such as fertilizer, which is shipped from a port of origin to a port of destination, or sand and gravel, which some companies mine from the river and then transport to a processing facility on shore. In addition, the Corps conducts river maintenance and habitat recovery projects, which require the shipment of waterway improvement material, such as stone or rock. In this context, Congress asked GAO to determine (1) the annual and total tonnage of commodity shipments for each state served by the Missouri River, and (2) the comparable tonnage of commodity shipments transported on the Mississippi River for states served by both the Missouri and Mississippi rivers.

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