OMAHA, Neb. (AP) — Flooding in the central U.S. on Friday swamped small towns, forced some residents along waterways to evacuate, threatened to temporarily close a nuclear power plant and shut down stretches of a major river and an interstate highway, foreshadowing a difficult spring flooding season.

The high water, prompted by a massive late-winter storm, 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 in many places over the weekend, according to...