Watch the history of hydropower plants in the United States

Date Published: June 16, 2025

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More than 4000 hydroelectric dams have been built in the United States since the late 19th century. They range in size from about 100 kW to the mammoth 6809 MW Grand Coulee Dam in the state of Washington. Hydropower represents about six percent of all-time additions to electric generation capacity from all sources. For the first half of the twentieth century, hydropower and coal were the dominant sources of electricity generation.

New hydropower capacity additions in the United States declined across the 20th century due to a combination of technical, economic, and environmental factors. By the mid-century, most of the best dam sites had already been developed, leaving fewer viable locations for large new projects. Rising environmental awareness and regulations beginning in the 1970s made permitting more difficult due to impacts on ecosystems, fish migration, and local communities. At the same time, the economics of hydropower became less favorable compared to other energy sources like natural gas and, later, renewables such as wind and solar, which are faster and cheaper to deploy.

Small-scale hydropower projects (<10 MW) are somewhat of an exception to the overall decline in new hydropower capacity. Interest in small-scale or “run-of-river” hydropower has persisted due to lower environmental impacts, quicker permitting, and opportunities to retrofit existing non-powered dams, canals, and other water infrastructure.

Electricity, History, Hydropower, Power Plants, Renewable Energy, United States

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