The leak was discovered over the weekend at the biogas plant operated by St1 Biokraft.
"It's a black sludge that has flowed out, so it covers the vegetation and has flowed outside the area. They need to collect as much as they can, because if it rains it will be carried into watercourses and further into the groundwater," Malin Engdahl, environmental manager at Mönsterås municipality, tells the newspaper.
The company is now trying to collect the manure and limit the risk of spreading it to nearby waterways.
The municipality has reported the company to the police for suspected environmental crimes.
