because of all the snow in the Northwest!!!!! The Missouri River starts flowing this way at the continental divide in Montana, then crosses through north and south dakota before it gets here. There are a number of dams along the way. Because of the excessive amount of snow melt and the recent very heavy rains upstream, they have to release water from the dams upstream so that they aren't overtopped. That would be much worse. The problem is we've had excessive rains too. So the ground is saturated and the river is already flooded. There isn't much choice. They probably could have released it less and sooner, but they didn't so there you go
We aren't the only place that will be flooded, towns upstairs will be flooded too