(ABC 6 News) – A fertilizer spill is being blamed for killing nearly 750,000 fish in a 50-mile stretch of the Nishnabotna river.

According to the Iowa Department of Natural Resources (DNR), approximately 1,500 tons of liquid nitrogen fertilizer was discharged into the drainage ditch of the river in March. The release occurred due to an aboveground storage tank left open for the weekend.

The DNR is now recommending the attorney general’s office to take over enforcement of the company responsible, NEW Cooperative, based in Fort Dodge.

Under Iowa law, anyone responsible for polluting the water without a permit is liable to pay for any damage caused to the wildlife of the Nishnabotna. Cleanup efforts at NEW Cooperative’s facility are ongoing.

Attorney General Brenna Bird has not responded to the DNR’s request for a lawsuit.