Debora MacKenzie warns that ISIS’s position on the Tigris and Euphrates rivers gives it the ability to cause unimaginable chaos in Iraq:
ISIS now controls several major dams on the rivers, for instance at Haditha and Samarra. It also holds one 30 kilometres north of Mosul that was built on fragile rock and poses a risk of collapse. It holds at least 8 billion cubic metres of water. In 2003, there were fears Iraqi troops might destroy the dam to wipe out invading forces. US military engineers calculated that the resulting wave would obliterate Mosul and even hit Baghdad.
ISIS has already used water as a weapon, in a smaller way. In late April ISIS stopped flow through the relatively small Nuaimiyah dam on the Euphrates in Fallujah, reportedly with the aim of depriving Baghdad and southern Iraq of water. It could also have been to block military approaches to the town. Instead, the river backed up and poured into an irrigation canal, flooding the town of Abu Ghraib and dozens of surrounding villages over 200 square kilometres. Five people died, and 20,000 to 40,000 families fled to Baghdad.