Excerpt from page 28 of the report entitled “Continental Energy Sector Issues” prepared for the National Round Table on the Environment and the Economy by the Canadian Energy Research Institute, March 2004.
Although electricity generated from water plants is relatively emissions free, significant amounts of methane are produced from the decomposition of plants in the flood areas. In addition to methane, hydropower can have significant environmental effects such as fish injury and impact on downstream water quality. By diverting water out of the water bodies for power, dams remove water needed for healthy in-stream ecosystems thereby disrupting the natural river flows. Dams also slow down the flow of the river. Many fish species, such as salmon, depend on steady flows to flush them down river early in their life and guide them upstream years later to spawn. Slow reservoir pools disorient migrating fish and significantly increase the duration of their migration.38 In addition, bacteria present in decaying vegetation can also change mercury, present in rocks underlying a reservoir, into a form that is soluble in water. The mercury accumulates in the bodies of fish and poses a health hazard to those who depend on these fish for food.
38International Energy Agency Implementing Agreement for Hydropower Technologies and Programs Annex III: Hydropower and the Environment: Present Context and Guidelines for Future Action. Volume I: May 2000. Pg. 9-12