Egypt's aridity and shortage of arable land are critical issues. Egypt is 97% desert and is therefore dependent on the Nile River for its existence. Only 5% of the land area in Egypt is actually occupied and less than 4% of the land is suitable for agriculture. Since such a small percentage of land is habitable, population densities in some areas along the Nile River are greater than 1,000 people per square kilometer. Soil fertility has declined because of over cultivation and agricultural land has been lost to urbanization and desert winds. The expanded irrigation of desert areas after completion of the Aswan High Dam in 1970 has increased soil salinity and aided the spread of waterborne diseases. As of 1994, 28% of Egypt's soils had been damaged by increased salinity. Rapid population growth is also straining natural resources as agricultural land is being lost to urbanization, desertification, and salination.