What is Hydropower?

Water is another very important energy resource. People, plants and animals all depend on water. Hydropower is energy that comes from the force of moving water. The word "hydro" means water. Hydropower is a renewable energy source too. The sun heats the oceans turning it into water vapor. This is called evaporation. When the water vapor rises it turns into clouds. The cold air above the earth mixes with the clouds and releases rain or snow called precipitation. This water cycle goes on forever making this a renewable energy source.

Hydropower is also a clean and environmentally friendly source of energy. There is no fuel to burn, so there are no harmful emissions released into the air.

Hydropower History

Since ancient times people have found ways to harness the energy produced by moving water. For example the water wheel was first used around 200 B.C. for tasks like grinding grain and irrigation. Over 2,000 years ago the Greeks used water as an energy source to turn water wheels for grinding wheat into flour. The running water would flow over the wheel into buckets attached to the wheel and force the wheel to turn. In the early 1800s, Americans and Europeans used water wheels in factories to power machines like saws in lumber mills.

Hydropower was later used to generate electricity. After the invention of the turbine in the early 1800s and the generator in the late 1800s, the first hydroelectric plant in the U.S. was built at Niagara Falls in 1879. Niagara Falls borders New York and Canada. The gravity caused the water from the high ground to fall to the lower ground over the dam into a reservoir. The energy force from the falling water was used to turn a turbine in the dam and generate electricity.


Today the United States is the second largest producer of hydropower, behind only Canada. There are 75,185 dams in the U.S., but less than 3 percent are used for hydroelectric generation. Between 8 percent and 12 percent of U.S. electrical generation and about one-fifth of the electricity produced around the world is produced by hydropower.