River stages on the Big Sioux River reached 17.8 feet, 3.6 feet higher than the previous record of 14.2 feet in June 1957. Record winter snowfall in Eastern South Dakota began melting and pouring into the Big Sioux River, and the snowmelt runoff was more than the river and many of its tributaries could handle. Water left the main river channel and flooded several locations in Moody County. Within 24 hours, water was pounding over the dam east of the Crescent Street bridge on the northern edge of town. Roads crossing the Big Sioux River and some of its tributaries became impassable, roads east and west out of Flandreau were closed, and residents in the Egan area were evacuated. In the days that followed, the National Guard filled sandbags and helped city crews build temporary levees to protect the wastewater treatment plant, one of the city's wells, and the pump house.