Steve Glazer, chair of the Sierra Club's Colorado River task force, sees the effects on western river basins. Because of the changes in temperature and in water quality, the native fish in the Colorado River are all threatened by the construction of dams. Juvenile fish are often stranded trying to make the journey to the sea. As reservoirs are filled, severe and immediate flooding leaves river ecosystems significantly altered, and sometimes devastated. But it's not just the species directly affected that are in danger.
Dams prevent the seasonal flooding that create species-rich flood plains.
And native species downstream often can't survive the colder waters released beneath a dam. Estuaries at the mouth of rivers, deprived of freshwater flow, are often devastated as well. As dam builders move into developing nations, large dams threaten some of the world's greatest remaining stores of biodiversity. And dams are part of a plan to build a 2,000-mile shipping channel into the Pantanal region of Brazil, one of the world's largest tropical wetlands. Fortunately, the project was indefinitely postponed in September 1997.