ABSTRACT
Dams and canals have enormous impacts on the health of tropical people, and even some impact on the health of those in cooler, temperate zones. In the Tropics, the creation of a reservoir containing a reliable supply of slowly moving water which persists during dry seasons, or the cascading of flow over a spillway during seasons of plenty, also create new and enormous habitats for certain aquatic insects and snails which spread human and animal diseases. The digging of enormous networks of irrigation canals and their complementary drains not only creates habitats for malaria mosquitoes and bilharzia snails, but it puts them in direct proximity to large numbers of people who come to farm the fields irrigated by these networks: the larger and more stable the reservoir, the more numerous the disease-bearing insects and snails; the more intensive the irrigation rotations, the more people needed to work the fields and the more intense the transmission of water-associated diseases. This is the nature of the impact of waterresource development on health in the Tropics, and it is most severe where waterassociated diseases are endemic.
