Fear the Flood: Americans to Prepare for Possible Iraq Dam Collapse

— -- Amid fears the “most dangerous dam in the world” could collapse unexpectedly, the U.S. government is urging Americans in Iraq to have a plan in place to escape the deluge that could drown Mosul and reach all the way to Baghdad.

The U.S. Embassy in Baghdad issued a “security message” Monday announcing that the government of Iraq “is preparing to initiate emergency maintenance operations to reduce the risk of failure” to the Mosul Dam, the maintenance of which was interrupted in 2014 as the terror group ISIS temporarily took control of the gargantuan infrastructure project.

The alert said the U.S. didn’t have “specific information that indicates when a breach might occur, but out of an abundance of caution, [officials] would like to underscore that advanced preparation and contingency plans for prompt evacuation offers the most effective tool to ensure safety.”

The Mosul Dam, built on a terrible foundation in the 1980s, requires “extraordinary engineering measures” to fill in holes that constantly grow in the foundation in order to keep the dam operational in the best of times, according to a U.S. Army Corps of Engineers (USACE) report in 2007.

For more than 30 years -- and through several periods of violent conflict -- the Iraqi government has managed to keep the dam upright by continuously pumping in literally tons of grout like an industrial version of the little Dutch boy, as a geotechnical expert who worked on the dam described it to ABC News in August 2014.

But if it were to collapse, U.S. officials said the result would be “catastrophic.”

“[T]he most severe impact of a dam failure would be [for] the City of Mosul, located 50 kilometers [31 miles] downstream of the dam,” said an urgent letter from David Petraeus, then-commanding general of the U.S. Army, and Ryan Crocker, then-U.S. Ambassador to Iraq, to then-Iraqi Prime Minister Nouri al-Maliki in 2007. “Assuming a worse case scenario, an instantaneous failure of Mosul Dam filled to its maximum operating level could result in a flood wave over 20 meters [65 feet] deep at the City of Mosul, which would result in a significant loss of life and property.” The flood estimates for Mosul in Monday’s security alert are similar to those laid out in the 2007 letter.

A 2011 report written by a USACE official and published in Water Power magazine estimated failure “could lead to as many as 500,000 civilian deaths.”

Though pro-Iraqi government forces were able to recapture the dam from ISIS, they have not been able to liberate the city itself, home to an estimated 1.5 million people, now under ISIS control. Beyond the wall of water that could engulf that city, floodwaters, albeit at a lower level, could reach all the way to Baghdad, more than 200 miles further down the Tigris, depending on the performance of another smaller dam further downriver.

In addition to flooding concerns, the dam is also a “key source” of power and water for the surrounding area, a State Department official told ABC News in 2014.

CLICK HERE to read the alert and the embassy’s suggested courses of action.