Officials with the Iowa Department of Natural Resources have been investigating a fish kill in Dubuque County.

Environmental specialists and fisheries staff began the probe on Monday. Investigators determined that manure runoff killed nearly 240 fish in a tributary that feeds into the Little Maquoketa River.

According to the DNR, investigators traced the manure runoff to Lawler Dairy Farm in Peosta. DNR officials said the farm's owners applied liquid manure to a nearby field. Snow melt and rainfall then caused the manure to run into a nearby ravine and into the unnamed tributary, located along Graff Road north of Peosta.

Charges against Lawler Dairy are currently pending, DNR officials said.