Hydroelectric reservoirs cover an area of the world the size of France. They release carbon dioxide and methane. Stagnant water produces the worst emissions because the decaying vegetation generates methane. This is 20 times as potent a greenhouse gas as CO2, which is produced when there is oxygen in the water. So a reservoir will produce more methane than the river did before the dam was built.
Dams can also be lethal to salmon .
Standing water in reservoirs facilitate unnaturally high water temperatures, and spillways raise the levels of nitrogen gas, both of which increase mortality in salmon runs. In this site's discussion group, Ola Mork says that looking at the sites posted earlier by Yuill, he could not find much in the way of primary sources for research on climate change. If anyone knows of a site that has links to research that is being conducted, please send them in. If climate change is happening as a result of humans, is it very important that primary sources be available as widely as possible, not just through the news media's interpretations. There is no question.