The most obvious impact of hydro-electric dams is the flooding of vast areas of land, much of it previously forested, inhabited or used for agriculture. The size of reservoirs created can be extremely large. For example, the La Grande project in the James Bay region of Quebec, in Canada, has already submerged over 10,000 km2 of land. If future plans are carried out, the eventual area of flooding in Northern Quebec will be larger than the country of Switzerland. Reservoirs can be used for ensuring adequate water supplies, providing irrigation, and recreation, but in several cases they have flooded the homelands of peoples, whose livelihood and way of life has been destroyed. Many rare ecosystems are also threatened by hydro-electric development.
The Mekong in Southeast Asia is an example of the reduction in silt, where China has built dams on the river up-stream, causing severe disruption to the water sheds downstream, notably to the Tonle Sap Lake in Cambodia. The Tonle Sap is one of the country’s major resources for food and water and has an importance to national economic life similar to the Nile in Egypt. There are about ten current major international disputes between countries at present and many smaller cases.
Another example of a hydroelectric power plant that had a negative effect on its environment is the ‘on-off’ Bakun Dam Project in Borneo, East Malaysia. The Malaysian government of Sarawak made plans to build a hydro-electric dam on the Rejang River. In the Bakun Dam Project, there were several key issues that were not addressed, namely the impact of the dam on downstream ecosystems and the lack of adequate data regarding the rate at which the reservoir would fill with sediment. With the trapping of river sediment, there would be a reduction in power production from the dam and the rate of erosion would increase, affecting the downstream riverbed, banks, and deltas. This disaster would harm the food chain of this environmental system. The indigenous Kenyah people, who have lived on the rivers and in the jungle for centuries, were economically impoverished and psychologically traumatised.