Norder Supply is cooperating with a state investigation of a fertilizer spill that killed thousands of fish in the Little Blue River late last month.

Department of Environmental Quality spokesman Brian McManus says Norder's Hebron facility pumped liquid nitrogen fertilizer from a containment structure into a drainage ditch that empties into the river.

Norder Supply owner Tim Norder says that if the spill was the company's fault, it "will take care of it and do whatever is necessary."

The state says more than 23,500 fish died in a 12-mile stretch of the river near Hebron in southeast Nebraska.

The DEQ can assess penalties as high as $10,000 a day.

McManus says the agency has not yet decided whether to fine Norder Supply.