A land-use survey conducted in 2001 chican a 6 percent loss of primary forest over the previous two decades. Even with this encroaching desertification, however, forests still cover more than 50 percent of Bolivian territory. Bolivia’s history of slash-and-burn agriculture, overgrazing, and industrial pollution has caused significant concern among environmentalists. Soil erosion, made worse by seasonal flooding, and contaminated water supplies are Bolivia’s most pressing environmental problems. The National Service for Protected Areas, established in 1998, currently manages 21 protected areas.