More than 80,000 people in the mountain community of Lynchburg, Virginia, were at risk, and 120 families evacuated, when rising waters from nearby College Lake reecently threatened to overflow its outdated dam. Although calamity was averted when the water receded, the incident was a frightening reminder of the growing risk facing millions of Americans. The average age of the 90,580 dams located across the U.S is 56 years, according to the American Society of Civil Engineers (ASCE). Worryingly, more than 15,000 of them are considered “high hazard” and – like the Lynchburg dam built in the 1930s – need to be repaired or replaced.