OMAHA, Neb. (AP) — Flooding in the central U.S. on Friday caused by rain and snowmelt from a massive late-winter storm forced hundreds of people to evacuate, threatened a nuclear power plant and shut down traffic on part of the Missouri River, foreshadowing a difficult spring flooding season.

The high water pushed some waterways to record levels in Nebraska, South Dakota, Iowa and Minnesota. The flooding was the worst in nearly a decade in places, though the situation was expected to improve quickly over the weekend, according to Mike Gillispie, National Weather Service hydrologist in Sioux Falls.

Flooding remained a big concern in the lower Missouri River region — which is a major source for the Mississippi River — with the weather service issuing warnings of high water along the river and its tributaries from southeastern South Dakota to St. Louis in Missouri.

The storm also significantly increased spring flood worries in the Red River Valley in the Upper Midwest, where the neighboring cities of Fargo, North Dakota, and Moorhead, Minnesota, experienced a record flood 10 years ago.

Iowa Gov. Kim Reynolds signed an emergency disaster proclamation and activated the state emergency operations center Thursday. South Dakota Gov. Kristi Noem opened that state’s emergency operations center and said an emergency declaration was being prepared.