![PDF version PDF version](https://www.americangeosciences.org/sites/all/modules/print/print_pdf/icons/pdf_icon.png)
Hydropower uses the energy from moving water to power machines or generate electricity. Used for over two thousand years in water mills, today hydropower is more commonly associated with electricity generation.
Basics
Hydropower uses the energy from moving water to power machines or generate electricity. Used for over two thousand years in water mills, today hydropower is more commonly associated with electricity generation. Hydropower has been used to generate electricity since the late 19th century, and remains the largest source of renewable energy worldwide.
Hydroelectric power plants are usually built inside dams. The reservoir of water that collects behind the dam provides a steady supply of water, which passes through giant turbines to generate electricity. Hydropower is particularly common in places with high rainfall and lots of topography, such as Washington and Oregon, which together produce around 40% of the hydroelectricity generated in the United States. Read more