Hydroelectric power is important for the nation, providing about 7% of total power without polluting water or air. However, it can have big environmental impacts by changing the environment and affecting land use and habitats. In the early 20th century, hydroelectric plants supplied almost half of the nation's power, but now it's down to about 10%. Most states in the US use some hydroelectric power, with states like Idaho, Washington, and Oregon relying on it the most. China leads the world in hydroelectricity usage with large facilities developed in the last decade.