A dairy farm in northeast Iowa faces penalties after a manure spill was discovered in the Little Maquoketa River.

The spill happened last weekend, but officials didn’t find out about it until Wednesay when someone reported seeing dead fish in the river. According to state officials, the spill was traced to the Lawler Dairy Farm near Graf, in Dubuque County. It’s owned by Jeff and William Lawler of Peosta. The manure spilled out of an earthen basin, onto a grass waterway, into a ravine and then into a tributary of the Little Maquoketa River.

The Lawlers dug a pit near the basin to try to contain the manure, but state officials directed the farmers to build a temporary dam on the tributary. That way the manure-contaminated water can be pumed out of the stream and onto a nearby pasture.

According to a statement released by the Iowa Department of Natural Resources, state officials will “pursue penalties for the spill” as well as for having an unregistered manure storage basin. The Lawlers also face a penalty for late reporting of a manure spill. The spill of any hazardous substance, including manure, is to be reported to the state within six hours.