To introduce perennial irrigation into an arid area means changing its micro-climate. The new moist ecosystem will attract all sorts of micro-organisms, insects and other forms of animal-life which are adapted to the new conditions. The species which previously lived in the arid area cannot adapt to the new moisture levels. Many of the new forms of live are undesirable, especially their numbers, and because they live off the crops which are being cultivated. They also lead to an upsurge in waterborne and other diseases, such as malaria, schistosomiasis, filariasis and river blindness. Migrant workers and relocated population in newly irrigated areas do not have adequate sanitation or housing, and so the local water supply becomes contaminated with human faeces. Under such conditions, epidemics, transmission of roundworm, hookworm, dysentry, hepatitis, cholera etc. will increase.