The Mosul Dam, which the US claim was tonight recaptured by the Kurds, could become a "weapon of mass destruction if it got into the hands of terrorists."
Islamic militants could blow it up if they managed to take it and send a torrent of water down the Tigress River.
But ITV News Diplomatic Correspondent John Ray said this was unlikely to happen as they would also flood their own positions.
Kurdish Peshmerga fighters have emerged victorious in the battle for Mosul Dam, but the question is - what will their next move be?
An ITV News team at Mosul Dam was with victorious Kurdish Peshmerga fighters at the complex earlier today.
ITV News joined a Kurdish unit fighting Islamist militants near Irbil and found them using tanks from the 1950s and short on ammunition.