How many dams in US are unsafe?

About 14,000 dams across the country are classified as “high-hazard” dams, meaning a dam failure or operational error could result in the loss of human life. In 2008 more than 2,000 of these high-hazard dams were also rated structurally “deficient,” meaning they were at serious risk of failure.



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More than 200 U.S. dams failed in downpours, floods and other wet weather since 2000, unleashing the water in their reservoirs to surge downstream, according to data kept by Stanford University. Many were smaller structures that presented less downstream danger than Oklahoma City's Overholser Dam.

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The Most Devastating Dam Failure in US History
  • The worst dam failure in the United States was the Johnstown flood of 1889. ©Everett Collection/Shutterstock.com.
  • The South Fork Fishing and Hunting Club is believed to be the cause of the dam's failure. ...
  • The Johnstown flood of 1889 killed 2,209 people.


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More than 2,000 dams have been removed in the U.S. as of February, with the bulk of those having come down within the last 25 years, according to the advocacy group American Rivers.

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The Colorado River has more dams than any other river in the United States. In total, there are 15 dams on the Colorado River, all of which are used to pool water for irrigation and generate electricity.

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Downriver towns and major cities would see the most damage, in the event of the dam's physical collapse. Water flows would engulf many towns and growing cities around Mohave county, including Laughlin, Nevada; Needles, California; Lake Havasu, Arizona; and even as far south as Yuma, Arizona, and San Luis Rey, Colorado.

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Together these factors have made Mosul Dam the most dangerous dam in the world, because there are almost certainly an unprecedented level of untreated voids in the dam's foundation.

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