Namibia's environmental concerns include water pollution and insufficient water for its population. The nation has 6.2 cubic kilometers of renewable water resources. About 68% is used in farming and 3% for industrial purposes. Only about 67% of the people living in rural areas have access to pure water. Nearly all of the urban population has safe water. The nation's cities produce about 0.1 million tons of solid waste per year. Deforestation and soil erosion also threaten the nation's land. Agricultural chemicals, such as DDT, are also a threat to the environment due to excessive usage. The Namibian Wildlife Trust, organized in 1982, works closely with the Department of Nature Conservation to maintain the habitat and to prevent poaching of threatened fauna and avifauna. In 2001, 12.9% of Namibia's total land area was protected. Twelve nature conservation areas cover 99,616 sq km (38,462 sq mi). Among these are the 22,270-sq-km (8,603-sq-mi) Etosha National Park, one of Africa's best-run and least-visited animal preserves; a smaller game park near Windhoek; and the Namib Desert Park (23,401 sq km/9,035 sq mi), east of Swakopmund. There is a seal reserve at Cape Cross, north of Swakopmund. As of 2001, 11 mammal species and 8 bird species are endangered. About 14 species of plants are threatened with extinction. UN sources have identified the black rhino, cave catfish, and the wild dog as endangered species. Burchell's zebra has become extinct.