"Hydro" means "water" in Greek - so "hydro power" is made from water.
It might sound odd that we can use water to make electricity because they're a dangerous combination, right? Actually, the water never comes in contact with the electricity. The water flowing down a river is used to spin the turbines inside the generator.
First hydro power plant in Appleton, Wisconsin
Photo courtesy of “dam across river, Appletown, Wis.,” 1880-1889. Prints and Photographs Division, Library of Congress.
People have used water power for more than 2,000 years. Ancient Egyptians used water wheels for grinding grain, and early Americans learned how to use them for sawing wood.
In the 1880s, scientists learned how to use a flowing river to spin the turbines of a generator. The first hydroelectric power plant in the U.S. opened on the Fox River near Appleton, Wisconsin, in 1882.
By the 1940s, nearly half of the electricity in the United States came from hydro power. After World War II, coal power plants became more popular.
Kilbourn Hydro in Kilbourn, Wisconsin
Most of the big hydroelectric power plants in the United States are in California, Oregon and Washington.
People built dams to control the power of the big mountain rivers. Workers can change the amount of water flowing through the dam depending on the weather and how much electricity people need.
The biggest hydroelectric dam in the United States is the Grand Coulee Dam in Washington. Started in 1933 and completed in 1942, it's the largest concrete structure ever built: 5,233 feet long and 550 feet high!
It has four power plants with 33 generators, making enough electricity for more than two million homes.
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