Americans in Iraq should be poised to leave at any minute—but not because of any terrorist threat. In a security alert, the US Embassy in Baghdad notes more than a million people could be drowned or left homeless if Iraq's largest hydro-electric dam on the Tigris River breaks apart near Mosul. The dam—built on a soft mineral easily eroded by water—has been impaired by structural flaws since it was built in 1984 and requires workers grouting around the clock to keep it strong, report the New York Times and Guardian. But when the Islamic State captured the dam for a two-week period in 2014, all work stopped. Few engineers returned when government forces recaptured it and regular maintenance couldn't continue. "It is going from bad to worse, and it is urgent," says a former engineer. "All we can do is hold our hearts."
An Italian company has been awarded a contract to make repairs, but they're expected to take 18 months and engineers say melting snow has pushed the reservoir to maximum capacity. Officials warn a breach could put Mosul under 70 feet of water within hours, reports Reuters. Cities including Tikrit, Samarra, and Baghdad could be flooded with 13 feet in a day. "We have no specific information that indicates when a breach might occur, but out of an abundance of caution, we would like to underscore that prompt evacuation offers the most effective tool to save lives of the hundreds of thousands of people," the US alert reads, advising Americans to keep three miles from the river. Iraq's government has downplayed the threat, noting the chance of a breach is "extremely small."