The energy in flowing water has been used by humans for thousands of years. The ancient Greeks fashioned water wheels to grind grain, and the pull of gravity on water, effectively harnessed in hydroelectric facilities, has served as a reliable source of power for commercial and industrial activities in modern times.
The twentieth century brought great technological innovations to the electric business, and dozens of dams captured the flow of some of America's largest rivers. The US Bureau of Reclamation built facilities across the country, most notably the western states, and the electricity, water, and recreational opportunities provided by those dams fueled much of the population and economic growth of that region.
Currently, about 10% of U.S. electricity comes from hydropower. While this energy source is clean and renewable, with no emissions, hydroelectric dams do have substantial impacts on river ecosystems. These large concrete structures block the natural flow of the water, preventing seasonal flooding, but also upsetting plant and animal life that depends on those annual cycles for life-giving nutrients. Fish that depend on unimpeded access to upper reaches of waterways for reproduction are blocked from spawning in their traditional areas, threatening their survival.
In addition, massive amounts of sediment have backed up behind America's dams in the past 50 years, reducing their capacity and concentrating various pollutants in very deep water that will be difficult to remove. While there are solutions to some of these problems, such as fish ladders beside dam spillways, new approaches such as micro-hydro projects with minimal environmental impacts have been the technologies of choice for the sustainable use of the world's hydro resources.
Information on Hydropower
US DOE Wind and Hydropower Program
National Hydropower Association:
Solar Energy International,
Light in the River
Pacific northwest fishery issues