Bombed, breached, hacked … dams have a long history as weapons of war, seized on or attacked for their capacity to wreak massive havoc and suffering.

Dams as weapons of warfare have emerged once again as a potential threat in the struggle for Iraq as control of water resources remains a key priority for all sides.

According to news from the region, Islamic State (IS) militants have gained control of dams on the upper reaches of Iraq’s two main water supply rivers, the Tigris and Euphrates. On August 7, IS succeeded in capturing Iraq’s largest dam, the Mosul, on the River Tigris, from the control of the Peshmerga forces of Kurdistan. Although, new reports say Peshmerga forces retook the eastern part of the dam early Sunday, backed by U.S. and Iraqi air strikes, and that fighting for advantage remains ongoing. Some reports estimate 80 percent of the dam has been taken back by the Peshmergas.*

It is feared that, under IS control, the Mosul could be used as an instrument of war – flooding farmland and disrupting drinking water supplies – as happened earlier this year when IS took over the smaller Fallujah dam in western Iraq’s Anbar province. [See also – Iraq crisis: How Islamic State could exploit the Mosul Dam]. Command of the Mosul not only gives the IS control over water flow into Baghdad and to the agrarian areas south of Baghdad, it also permits IS the option of  imposing a famine on the rest of Iraq, if it chooses.

To make matters worse, the Mosul, “is essentially a ticking time bomb,” Azzam Alwash, an Iraqi hydraulic engineer, told the Wall Street Journal on August 11. Built on a soluble gypsum base, the dam has required constant grouting since its completion in the 1980s – a highly skilled process involving injections of grout concrete into the dam’s base around six times a week to prevent water seepage and dam failure. If not attended to, the bedrock beneath the Mosul could dissolve, triggering collapse and catastrophic flooding, possibly resulting in a worst-case scenario flood wave of 20 metres (65.5ft) deep at the city of Mosul with a population of 1.5 million people; an event that would also flood Baghdad.

“I can’t speak to the skill of the insurgents, but I’d imagine that they might have some trouble with this,” Richard Coffman, an assistant professor of civil engineering at the University of Arkansas, who has conducted research on the Mosul Dam, told Business Insider.

The US Army Corps of Engineers, which advised the Iraqi government on the structure, called it “the most dangerous dam in the world.”

Taking control of water and power supply is a core military tactic of battles throughout history in order to gain a powerful war advantage. In the case of dams, cash can be amassed from the takeover of hydroelectric facilities in return for continued water and power supply, or shut off to ensure deprivation and hardship. Dams throughout time have also been attacked or commandeered to flood enemy territory, civilian populations and farmland; resulting in loss of life, shelter, food and safe drinking water. The largest act of environmental warfare in history occurred in June 1938 when the Chinese Nationalist army breached the country’s Yellow River dikes in an attempt to prevent Japanese invaders from attacking the city of Zhengzhou and endangering the headquarters of the Nationalist government in neighbouring Wuhan. The strike flooded three thousand square kilometers of farmland across several provinces and killed an estimated 80,000 people who either drowned or perished in the aftermath, but did not stop the Japanese army from taking over Wuhan on October 25, 1938. [For a historic overview of dams as weapons of war, see: Dam Warfare].

* Update to this story: As of Tuesday, August 19, 2014, Iraqi and Kurdish ground forces, backed by U.S. air strikes, recaptured the Mosul; a struggle made more difficult by booby traps Islamic State militants had lain, rigging part of the area with a complicated network of landmines and remotely triggered bombs.