Anaerobic lagoons are use to dispose of animal waste, particularly that of cows and pigs. The waste is washed into the lagoon by flushing the animal pens with water. Solid waste, particularly the fibrous type of cows, is sometimes separated before the wastewater enters the lagoon to prevent the buildup of solid material. Anaerobic organisms naturally present in the manure and the environment decompose the waste in the anaerobic conditions of the lagoon.