Hydroelectric power is produced by the conversion of the energy of flowing water to mechanical energy, which is then converted into electricity by a generator. Hydroelectric power is produced at dams where there is a sufficient drop in elevation. The moving water turns a turbine, which turns a generator shaft, which produces electricity.
Hydroelectric power is considered a renewable energy source, and produces almost no carbon dioxide or other greenhouse gasses through its production of electricity. It does not rely on fossil fuels. However, hydroelectric dams can cause disruption to ecosystems that can have significant environmental impacts.
In the United States, most hydroelectric power is generated and used in the Pacific Northwest, due to the availability of natural resources.