ERBIL, Kurdistan -- When the Islamic State, also known as ISIS, swallowed large swaths of territory in Iraq, they also captured what might be the biggest "weapon" of all: Iraq's largest dam.
The nightmare scenario for the world has been a terror group getting its hands on a weapon of mass destruction.
Now, just a two-hour drive from Erbil in northern Iraq, ISIS has done just that. When it captured the Mosul Dam, experts knew the group had a new weapon in its terror arsenal.
Kurdish civil engineer Adwa Jaji said terrorist control of the dam is a frightening prospect.
He explained that the huge structure, which in the best of times has been called "the most dangerous dam in the world," now represents a ticking time bomb in the hands of ISIS.
Watch how far the water would reach if the Mosul Dam broke.
"I think now it's too dangerous," Jaji told CBN News. "Even if not blasted by ISIS, the dam will destroy itself because there is nobody to rehabilitate it."
Jaji said the poorly designed dam is built on unstable soil that needs periodic infusions of grout to stabilize it.
"One, it is not resisting earthquake and vibration forces. The dam is not built to resist these two types of forces," Jaji explained.
And if ISIS fails to maintain the dam, it could burst. Jaji said if the dam -- located above Mosul -- bursts, it would send a 60-foot-high wall of water toward Mosul, which could reach all the way to Baghdad.
"According to the information we have, maybe 500,000 [to] 600,000 people [could be] killed in one day," he said.
Jaji said an international effort should be made to recapture and secure the dam. Even if ISIS does not destroy it, the group could hold the country hostage with the threat of an ecological disaster.
In the meantime, the United States continues its humanitarian air drops to the stranded Yazidis and its airstrikes against ISIS positions, as more information surfaces about the group.
Peshmerga commanders on the front lines told CBN News that ISIS often begins its attacks when suicide bombers drive into their positions. The commanders said when ISIS takes over a town, their fighters often come in like a lamb but soon become a wolf.
"First of all, they don't do anything. They say 'calm down until things get better' and then when they have full control of an area…they start killing people," one commander said.
ISIS terrorists threatened one Iraqi man who works at a power plant, saying "if you personally are not giving back the electricity, we will destroy your family."
The terrorists' barbarism is also being passed down to the next generation, as evidenced by the photo of an Australian boy holding the severed head of a Syrian soldier that's gone viral. The boy's father, an ISIS fighter, added the caption, "That's my boy!"
"It's just so hard to hear all these stories and imagine a human being doing this. It's so hard," Dr. Sarah Ahmed, with the Foundation for Relief and Reconciliation in the Middle East, told CBN News. "It's the work of the devil."