Hydropower, also referred to as hydroelectric, is the nation's second largest source of renewable energy, accounting for about 2.5% of the nation's energy supply and about 7% of the nation's electricity. The amount of hydropower available annually varies largely due to changes in precipitation. Many of the most effective locations to build large dams have already been used, limiting the amount of new dams that can be built. Although hydropower is a clean energy source compared to fossil fuels in terms of emissions, hydropower affects the environment in other ways, such as interfering with the movement of fish, affecting downstream water quality and flow, and altering sediment flow in rivers.


  • The three types of conventional hydropower plants:
    • The most common type of hydroelectric power plant is an impoundment facility. An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level.
    • A diversion - sometimes called run-of-river - facility channels a portion of a river through a canal or penstock. It may not require the use of a dam.
    • When the demand for electricity is low, a pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.
      Read more at the  Department of Energy Energy Efficiency and Renewable Energy Hydropower Page.
  • Dams have other benefits such as recreation, stock/farm ponds, flood control, water supply, and irrigation.
    Read more at the  Department of Energy Energy Efficiency and Renewable Energy Hydropower Page.
  • The Department of Energy is currently researching micro dams that would generate up to 1MW of electricity (small dams generate up to 30MW). Since they would require less water and take up less space, they could be used to power a farm, ranch, or small village, and would have less of an impact on the environment.
    Read more at the  Department of Energy Energy Efficiency and Renewable Energy Hydropower Potential.
  • New and innovative ways are being discovered to harness hydropower: Two emerging categories of renewable energy technologies - hydrokinetic and wave energy conversion devices - offer ways to tap the energy of moving water without dams or other methods used by conventional hydropower facilities. These technologies include devices designed to be used in natural streams, tidal estuaries, ocean currents, and constructed waterways, as well as devices designed to capture the energy of ocean waves.
    Read more at the  Idaho National Laboratory.