marbled teal, have provided water for agricultural irrigation for at least 5,000 years. They are fed by the Helmand and Farah rivers, which ran at 98% below average in drought years between 2001 and 2003. As in other areas of the country, the loss of natural vegetation resulted in soil erosion; here, sandstorms submerged as many as 100 villages by 2003. Some of the major water reservoirs and dams include the following: Band-e Amir in Bamyan Province Dahla Dam in Kandahar Province Darunta Dam in Nangarhar Province Kajaki Dam in Helmand Province Kamal Khan Dam in Nimruz Province Naghlu Dam in Kabul Province Qargha Reservoir in Kabul Province Salma Dam (Afghan-India Friendship Dam) in Herat Province Sardeh Dam between Ghazni Province and Paktika Province Pollution Since 2002, over 5 million Afghan citizens living in Pakistan and Iran have returned to Afghanistan. Many of them settled in the big cities, particularly in Kabul, Kandahar, Herat, Mazar-i-Sharif and Jalalabad. Air pollution Air pollution in Afghanistan's major cities is becoming a serious problem to public health. Residents of Kabul suffer the most from air pollution. Over 2,000 Kabul residents die from air pollution each year. Large number of vehicles in the city is the main reason for this. Nationally, an estimated 5,000 people die from air pollution. Some sources have given a much higher number of deaths in the past. Vehicles are also blamed for the air pollution in the other cities. Domestic and industrial waste Afghanistan has long lacked a proper sewage system. In 2002, the United Nations Environment Programme found that a lack of waste management systems was creating dangerous conditions in several urban areas. In Kabul's districts 5 and 6, household and medical waste was discarded on streets. Human waste was contained in open sewers, which flowed into the Kabul River and contaminated the city's drinking water. Urban dumpsites have been used in lieu of managed landfills in Kabul, Kandahar and Herat, often without protection of nearby rivers and groundwater supplies. Medical waste from hospitals is sometimes disposed in the dumpsites with the rest of the cities' waste, contaminating water and air with bacteria and viruses. Lack of sewage management is not unique to Kabul. In urban areas, open sewers are common while wastewater treatment is not. Much of the urban water supply is contaminated by Escherichia coli and other bacteria. Oil refineries are another source of water contamination. In