BROWNVILLE, Neb. (AP) — A utility has issued a required safety notification as it continues to add sandbags to the levee that protects its nuclear power plant along the swollen Missouri River in southeast Nebraska. The Nebraska Public Power District declared a “notification of unusual event” Friday at its Cooper Nuclear Station near Brownville, about 59 miles (95.5 kilometers) south of Omaha. The notification was required because the river level reached 42.5 feet.

The notification is the lowest and least serious of four emergency classifications established by the Nuclear Regulatory Commission for nuclear power plants. The district says it means simply that: Conditions are not ordinary. The plant continues to generate power. The river’s rapid rise is fueled by snowmelt and storm runoff from a late-winter weather system that brought powerful winds and heavy rainfall to the eastern side of the state this week.

District spokesman Mark Becker told the Omaha World-Herald on Thursday that if the river hits the level of 45.5 feet projected by the National Weather Services this weekend, the plant would have to be shut down.