The Carroll County Bureau of Utilities says about 150,000 gallons of partially treated wastewater have overflowed into Piney Run Creek at the Hampstead Wastewater Treatment plant.
Utilities officials say heavy rain caused Wednesday morning's overflow.
Over the past four years, repairs were made to areas of infiltration. The Bureau of Utilities says that had these repairs not been made, the overflow would be been much worse.
Health officials were notified of the overflow and signs have been posted at the creek telling people to avoid contact with the water.