Council of Canadians chairperson Maude Barlow has written about dams in both Blue Covenant: The Global Water Crisis and the Coming Battle for the Right to Water and Blue Gold: The Battle Against the Corporate Theft of the World's Water. She writes that -- more than forty-five thousand large dams (higher than 15 meters) have been built around the world at a cost of around US$2 trillion. While dams can provide some benefits, such as electricity, supplying water, controlling floods and facilitating navigation, much evidence suggests that these are benefits of smaller dams. But major dams around the world:
1. ARE A SOURCE OF GREENHOUSE GAS EMISSIONS: Large dams trap organic materials and rotting vegetation from submerged lands, which in turn creates methane gas, a major source of greenhouse gas emissions. Global warming is one of the greatest threats to freshwater resources. It has been estimated that hydropower dams in the Amazon cause far more global warming than modern natural gas plants generating the same amount of energy.
2. HARM INDIGENOUS PEOPLES: Indigenous peoples have been disproportionately hurt by the construction of mega-dams and water diversion projects.
3. CAUSE MERCURY POISONING: The drowning of land vegetation creates the habitat required by the bacteria that absorb any mercury that happens to be in the soil. The reservoirs convert this mercury into a form that fish can ingest and mercury then enters the food chain. It bioaccumulates, and can be many times more lethal by the time humans eat it than in its original form. (This is how the Cree of northern Quebec came to have such high levels of mercury in their systems. When they ate fish from the waters diverted for the massive James Bay hydroelectric project, 64 percent of the Cree in the area took in unsafe levels of this poisonous element. Mercury poisoning can cause blindness, reproductive failure, and brain damage.)
4. DISRUPT RIVERS: Big dams disrupt river flow patterns. Sixty percent of the world's major rivers have been fragmented by dams and diversions, and more than a million square kilometres - 1 percent of the world's land surface - have been inundated by reservoirs worldwide. (In Canada, more stream flows are diverted out of their basins of origin than in any other country in the world - by a considerable margin.)
5. DISRUPT AQUATIC HABITAT: Big dams disrupt aquatic habitat, reducing biodiversity. Big dams and diversions are the main reason why one-third of the world's freshwater species are extinct or endangered. Large dams are also the reason why so many of the world's great rivers no longer reach the ocean, and why rich delta areas, where freshwater meets seawater - the home to so many species - have been destroyed.
6. DISPLACE PEOPLE: They displace huge numbers of people due to their size. Close to eighty million people have been forced from their lands to make way for dams and few have been compensated.
7. CAN CAUSE EARTHQUAKES: The tremendous weight of water in a basin not designed to hold it deforms the earth's crust beneath it, sometimes causing earthquakes. There is now documented evidence linking earth tremors to some 70 dams. In fact, the shift of weight when so much water is moved by human technology is affecting the earth's rotation. Geophysicists believe that dams have slightly altered the speed of the earth's rotation and the shape of its gravitational field.
8. CAN LEAD TO EVAPORATION: They greatly multiply the surface area of water exposed to the sun, dams, especially in hot climates, can also lead to the evaporation of huge amounts of water. About 170 cubic kilometres of water evaporate from the world's reservoirs every year, almost one-tenth of the total amount of fresh water consumed by all the world's major human activities. Consequently, salt is left behind in unnatural amounts, and this high salinity in many of the world's major rivers destroys wetlands and aquatic life and renders the surrounding soil unusable.
9. REQUIRE PRE-CONDITIONS: Conditions for the construction of any dam should include: transparency of process; exploration of more environmentally sound alternatives; environmental, social and economic impact assessments; accountability to local people who have the right of veto; full financial compensation to displaced persons; ecosystem protection; protection of local food supplies; guarantee of local health protection; and the inclusion of environmental and social costs in any economic forecasts.