Algeria's principal environmental problem is encroachment of the desert onto the fertile northern section of the country. Soil erosion from overgrazing adds to the effect. To impede desertification, the government in 1975 began a project to erect a "green wall" of trees and vegetation 1,500 km (930 mi) long and 20 km (12 mi) wide along the northern fringes of the Sahara. The annual cost of this 20-year afforestation project was about $100 million.
Other significant environmental problems include water shortages and pollution. The small amount of water available in Algeria is threatened by regular droughts. The problem is further complicated by lack of sewage control and pollutants from the oil industry, as well as other industrial effluents. The Mediterranean Sea has also been contaminated by the oil industry, fertilizer runoff, and soil erosion.
Endangered or extinct species include the Barbary hyena, Barbary leopard, Barbary macaque, and Mediterranean monk seal. Of the 92 species of mammals, 15 were threatened as of the late 2001, as well as eight of the 192 species of birds.