Water is stored up behind the dam and released through the turbines when power demand is greatest. This causes water levels to fluctuate widely on both sides of the dam, stranding fish in shallow waters and drying out the habitat. In most cases, nature loses out to boaters and electric customers. The risk of a dam breaking should not be ignored. In northern India and Nepal, in the Himalayas, huge hydroelectric projects are planned that would create large reservoirs in a geographically unstable region.
Frequent earthquakes make the dam a risky venture for heavily populated areas downstream.
This is compounded by the fear that large, heavy reservoirs would put additional pressure on the plates in the region, causing even more earthquakes. Another cause of dam breakage has so far never occurred, but came close during the Gulf War. One Iraqi target considered by American bombers in the war was the hydroelectric dam upstream from Bagdad. Since too many civilian casualties would have resulted, the dam was spared. Conclusion The environmental impacts of large hydropower can be immense.