Almost 4,100 dams are categorized at the same risk level and condition — or worse — according to an NBC News analysis of the inventory’s data. Every state has at least one such dam. Ohio has the most at 373.

As a whole, America’s dams — more than 91,000 in total — are aging. Many need expensive rehabilitation. Few were designed for today’s climate, with a warmer atmosphere that can hold — and dump — more water. The number of people living in inundation zones below these dams continues to grow.

Dams in distress: Partial failure in Minnesota offers a nationwide warnin