'Catastrophic': US Raises Alarm Over Perilous Mosul Dam

US previously described massive structure as "most dangerous dam in the world."

— -- The U.S. Ambassador to the United Nations today left a “chilling” briefing about the danger posed by Iraq’s Mosul Dam and called on the international community to realize the “magnitude of the problem and the importance of readiness to prevent a humanitarian catastrophe of epic proportions.”

The briefing from geotechnical experts said the dam, already described nearly a decade ago as the “most dangerous dam in the world,” now faces a “serious and unprecedented risk of catastrophic failure with little warning."

In a worst case scenario, should the dam breach, it could send a flood wave several stories high into Mosul and inundate cities with devastating effect as far down the Tigris as Baghdad, more than 200 miles away, according to a 2007 warning letter from top U.S. officials to the Iraqi government and contemporary estimates by experts.

Last week, the U.S. Embassy in Baghdad issued a “security message” that noted that while officials did not have “specific information that indicates when a breach might occur,” it advised Americans in the potential danger zone to have an evacuation plan ready.

The day after the security message was sent out, an Italian company, Trevi, announced that it had agreed to intervene and fix the dam for $300 million, but it won’t be easy.

“These are huge and very sophisticated repairs. It’s not like going to Home Depot and grabbing some paint and caulk,” a geotechnical expert, who previously worked on the dam, told ABC News.

The expert said he foresaw a few months before meaningful repairs would begin. In the meantime, as to when the dam could fail, he said, it “could be tomorrow, could be next week, could be 10 years-time.”