Officials in three South Dakota cities are asking residents to leave their homes because of threatening floodwaters.
"As the water flow increases, we want to make sure we protect human life as we evaluate how the levees are doing, how fast the water is being released and whether the areas are going to be safe," Gov. Dennis Daugaard said.
Record rainfall in the northern Plains has forced the Army Corp of Engineers to release excess water from Missouri River dams.
In Dakota Dunes, people are building sandbag walls around their homes as others pack up belongings.
Engineers are building makeshift levees along the Missouri River, using Blackhawk helicopters to drop 2,000-pound bags of sand. Officials say flooding could last into July.
Meanwhile, other western states are also dealing with major flooding.
North Dakotans living along the Souris River are evacuating their homes in the face of rising waters. And in Montana, Gov. Brian Schweitzer has declared a major disaster in that waterlogged state.