The Gambia's environmental concerns include deforestation, desertification, and water pollution. Deforestation is the most serious problem, with slash-and-burn agriculture the principal cause. In the 1950s, 34,000 hectares (84,000 acres) were set aside as forest parks, but by 1972, 11% of these reserves had been totally cleared. As of 2001, only 2% of the total land area is protected. During 1981–85, deforestation averaged 2,000 hectares (5,000 acres) per year. Only 9% of the forests in The Gambia have survived the expansion of agricultural land and the use of trees for fuel. A 30% decrease in rainfall over the last 30 years has increased the rate of desertification for The Gambia's agricultural lands. Water pollution is a significant problem due to lack of adequate sanitation facilities. Impure water is responsible for life-threatening diseases that contribute to high infant mortality rates. The Gambia has 3 cubic kilometers of renewable water resources with 91% used for farming activity. Only about 53% of the people in rural areas have pure drinking water. As of 1994, The Gambia's wildlife was threatened by changes in habitat and poaching. As of 2001, 4 of the nation's 117 mammal species and 1 in a total of 280 bird species were threatened. One type of reptile was also endangered. Threatened species include the African slender-snouted crocodile and the West African manatee.