Since most of Algeria is desert or semi-desert, over 90% of the population is forced to live on the remaining 20% of land. The desert is moving northward. Vegetation has been stripped for use as firewood and animal fodder, leaving fragile soils exposed which then require expensive specialized care to conserve them. Water purification techniques are below standard and rivers are being increasingly contaminated by untreated sewage, industrial effluent and wastes from petroleum refining.
