Earlier this month, a major dam along Ukraine’s Dnipro River in Kherson province – the de-facto dividing line between Ukrainian and Russian forces on the war’s southern front – was destroyed, creating a humanitarian catastrophe. A deluge of water turned towns and streets into a detritus-filled swamp.

But this was not the first time that water has been weaponized in this war. With hydropower an important resource in a region starving for energy, and with self-styled volunteer forces taking command in local “oblasts,” water has become one of the war’s most important assets. That makes dams critical infrastructure on par with nuclear power plants.

It is hard to imagine a type of warfare more unconventional or prehistoric than “hydraulic warfare”— that is, the deliberate flooding during combat. True, this kind of warfare is not new, but an age-old technique used to enhance defenses. During the Eighty Years’ War, Dutch rebel led by William of Orange intentionally flooded low-lying areas to defend against the Spanish invaders. The Chinese breaching of Yellow River levees in 1938 to slow down the Japanese advance was called “The Largest Act of Environmental Warfare in History.”

During World War II, Josef Stalin directed his secret police to blow up a hydroelectric dam in the Ukrainian city of Zaporizhzhia to slow the German advance. The corresponding flooding was estimated to have killed upwards of 20,000 people caught in its path. Thus, flooding rivers can create a very effective defense but it can also