MARINETTE, Wis. -- Sludge poured from an overturned tanker truck in downtown Marinette on Tuesday.

The truck from the city’s wastewater treatment plant overturned, spilling about 4,000 gallons of industrial sludge in front of the Marinette County courthouse and city hall.

When firefighters arrived on the scene, the sludge was pouring out of a large hole in the tank. Officials said some of it went down a storm drain.

Crews spent about four hours cleaning up the mess before they could reopen the street.

The driver of the truck suffered minor injuries. Police said they don’t know what caused the truck to overturn.