There are over 77,000 dams of significant size (over 6 ft
[1.8 m] tall) in the United States, and tens of thousands of additional uncharted smaller dam structures. Constructed for the purposes of harnessing water resources for irrigation, water supply, and hydroelectric power, dams can be a useful ally for human needs; they also have a major and long-term impact on the entire river ecosystem.

Since 1912, over 460 dams have been removed from United States waterways for both safety and environmental reasons. Dams associated with hydroelectric power projects are decommissioned after their useful life and removal is often recommended to return river ecosystems back to their natural state.

Damaged or obsolete dam structures may present a safety hazard, particularly if they are no longer regularly maintained. Upkeep of a dam is expensive, and local taxpayers may bear the brunt of caring for a dam that no longer serves any practical...