Almost all fertile land is already under cultivation, and continued population pressure raises the threat of soil erosion and exhaustion, as well as infringement on forest resources for agricultural purposes. The demand for firewood has significantly depleted the timber stock. Malawi has 17.5 cu km of renewable water resources with 86% used for farming and 3% used for industrial activity. About of 95% city dwellers and 44% of the rural population have access to pure water. The nation's cities produce about 0.2 million tons of solid waste per year. Human encroachment has reduced wildlife habitats. The preservation of Malawi's wildlife is a significant environmental issue. As of 2001,8.9% of the country's natural areas are protected. Some of the nation's fish population is threatened with extinction due to pollution from sewage, industrial waste, and agricultural chemicals and siltation of spawning grounds. Also as of 2001, seven of the nation's mammal species and nine of its bird species were threatened, as well as 46 plant species. Threatened species include the African elephant, cheetah, and African wild dog.