Energy.gov

Most people associate water power with the Hoover Dam—a huge facility harnessing the power of an entire river behind its walls—but hydropower facilities come in all sizes. Some may be very large, but they can be tiny too, taking advantage of water flows in municipal water facilities or irrigation ditches. They can even be “dam-less,” with diversions or run-of-river facilities that channel part of a stream through a powerhouse before the water rejoins the main river. Whatever the method, hydroelectric power is much easier to obtain  and more widely used than most people realize. In fact, all but two states (Delaware and Mississippi) use hydropower for electricity, some more than others. For example, about 74 percent of Washington State’s electricity comes from hydropower. 

Additionally, hydropower costs less than most energy sources. States like Idaho, Washington, and Oregon, that get the majority of their electricity from hydropower, have energy bills that are lower than the rest of the country.  

Hydropower technologies generate power by using a dam or diversion structure to alter the natural flow of a river or other body of water. The Department of Energy's "Hydropower 101" video explains how hydropower works and highlights some of the Water Power Program's efforts in R&D in this area (to see how  a hydroelectric system works, see our How Hydropower Works page):

Learn the basics about hydropower (also called hydroelectric power):

• How Hydropower Works
• Benefits of Its Use
• Hydropower Use Throughout History