There is a powerful symbolism in the impending collapse of Iraq’s Mosul dam. Built on the cheap by Saddam Hussein in the early 1980s, it holds back up to 2.9 trillion gallons, roughly twice as much as Lake Pontchartrain in New Orleans. We all know what happened when Hurricane Katrina breached the levees around Pontchartrain’s south shore in 2005.

No hurricane is needed to breach the Mosul dam. Built on a weak foundation of soluble gypsum, its stability has always depended on continuous grouting. In 2007 the US Army Corps of Engineers, alarmed by what they had found after the invasion of Iraq, carried out repairs. But since the withdrawal of American forces, the dam has deteriorated. For several weeks in 2014 it came under the control of the Islamic State. Fighting between ISIS and Kurdish Peshmerga forces is just one of the reasons the dam has fallen into disrepair. A contract with an Italian engineering company to overhaul the dam has only just been signed by the Iraqi government.

Not for nothing did US Army engineers call Mosul “the most dangerous dam in the world.” According to Samantha Power, the US ambassador to the United Nations, a breach could send a 45-foot high wave down the River Tigris, killing between 500,000 and 1.5 million people. It would, Power said, be “a humanitarian catastrophe of epic proportions.”