High Quality Content by WIKIPEDIA articles! The 2011 Missouri River floods was a flooding event on the Missouri River in the United States. The flooding was triggered by record snowfall in the Rocky Mountains of Montana and Wyoming along with near-record spring rainfall in central and eastern Montana. All six major dams along the Missouri River released record amounts of water to prevent overflow which led to flooding threatening several towns and cities along the river from Montana to Missouri; in particular Bismarck, North Dakota; Pierre, South Dakota; Dakota Dunes, South Dakota; South Sioux City, Nebraska, Sioux City, Iowa; Omaha, Nebraska; Kansas City, Missouri; Jefferson City, Missouri, as well as putting countless smaller towns at risk. According to the National Weather Service, in the second half of the month of May 2011, almost a year`s worth of rain fell over the upper Missouri River basin. Extremely heavy rainfall in conjunction with an estimated 212 percent of normal snowpack in the Rocky Mountains contributed to this flooding event.