Dam security

20% of dams in populated areas lack emergency plan

As the nation's 84,000 dams continue to age, a growing number of people downstream are at risk, experts say.

That's not only because of older infrastructure but also because of population growth around some of the dams. More than a quarter were developed primarily for recreational purposes, according to National Inventory of Dams data from 2016.

"The nation’s dams are aging, and the number of high-hazard dams is on the rise," according to a 2013 report from the American Society of Civil Engineers. "Many of these dams were built as low-hazard dams protecting undeveloped agricultural land. However, with an increasing population and greater development below dams, the overall number of high-hazard dams continues to increase."