Aerial view of ash pond on the edge of a forest, Bosnia and Herzegovina. After coal is burned in power plants, the waste ash is mixed with water and pumped through pipelines into sludgy lagoons commonly known as ash ponds. The ponds are used as landfill to prevent the release of ash into the atmosphere, but they also contaminate the environment with toxic pollutants harmful to human health. The vivid colour of the pond indicates the presence of chemicals used to neutralise the wastewater.