Hydro-electric power harnesses the kinetic energy of falling or flowing water to drive turbines that generate electrical energy without air pollution or the need for fuel. While providing reliable low-cost power, large hydroelectric dams require flooding valleys that can impact habitats and species and have high initial costs. The Roosevelt Dam in Arizona and Hoover Dam on the Colorado River are two major hydroelectric dams that have supplied power to several western states for decades.

1. Hydro-electric Power. By Hayley Proudfoot & Jenny Arnold.