All of these human uses take their toll on freshwater ecosystems. The scale and extent of human impacts on freshwater systems have risen sharply in recent years. Freshwater withdrawals from rivers, lakes, reservoirs, underground aquifers and other sources have increased more in Asia during the past century than in other parts of the world. From 1950 to 1995, water use in Asia increased by almost 300 per cent. This rapid rise in demand has resulted in the proliferation of dams and reservoirs and the channelization of rivers.
Agriculture accounts for the major part of water withdrawals, mainly for irrigation.
In the more industrialized countries agriculture accounts for up to 50 per cent of withdrawals, but this figure rises to more than 90 per cent in all South Asian countries except Bhutan. In common with other parts of the world, the exploitation of water resources in the Asia and Pacific region has caused major disruption to river flow patterns. River levels and water tables are falling steadily and wetlands are increasingly depleted. Contamination by pollutants has seriously degraded water quality, reducing the amount of clean water available. In addition, rapid population growth has resulted in a decline in the annual per capita availability of freshwater in the developing countries of the region.