Deforestation is caused by farming activity and the nation's dependency on wood for fuel. By 1985, 3,701 sq km (1,429 sq mi) of forestland had been lost. The DROC has nine national parks. As of 2000, there were five Natural World Heritage Sites and three biosphere reserves, and 4.3% of the DROC's total land area was protected. The main environmental problem is poor water and sanitation systems, which result in the spread of insect- and rodent-borne diseases. The water is polluted by untreated sewage, industrial chemicals and mining by-products. The nation has 935 cu km of renewable water resources with 23% used for farming activities and 16% used for industrial purposes. Roughly 89% of city dwellers and 26% of the people living in rural areas have pure drinking water. In 2000, 38 of the DROC's mammal species and 26 of its bird species were endangered as well as 69 species of plants. Endangered or extinct species in the DROC include the Marunga sunbird and the northern white and northern square-lipped rhinoceros.