Russia and Ukraine have blamed each other for the breach.
"The Russian occupation troops destroyed the Kashkova hydroelectric station," said the Southern Command of Ukraine's forces on its Facebook page. "The scale of the destruction, the speed and volumes of water, and the likely areas of inundation are being specified."
Drone footage shows water gushing from the reservoir after the dam was breached.Screenshot/Twitter/@ZelenskyyUa
The Russian mayor of the occupied Novaya Kakhovka region, Vladimir Leontyev, told state media that the dam was destroyed as part of a "terrorist act," a term often used by the Kremlin to describe Ukrainian attacks.
The direct consequences of the breach aren't immediately clear. The Kakhovka Reservoir holds around 18.2 cubic kilometers of water, or 4 trillion gallons.
The reservoir serves as the primary water supply for cooling the Zaporizhzhia nuclear plant, which is further to the north-east and is also controlled by Russia.
The Kakhovka Reservoir also supplies water to millions of people in Crimea, which was annexed by Russia in 2014.
The dam's destruction will likely have a significant impact on Ukraine's anticipated big counteroffensive, according to Mark Hertling, former Commanding General of the United States Army Europe and the US Seventh Army.
Dozens of cities on both sides of the Dnipro will be flooded in the next 24 hours, tweeted Hertling.
A worst-case illustrative model of the dam's breach, created by Swedish outlet Cornucopia in October, shows significant flooding across Kherson, home to hundreds of thousands of people.
"In five hours, the water will reach a critical level," he said in a video.
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Blowing up the dam likely constitutes a war crime, according to the Geneva Conventions. The Conventions allow exceptions for such an attack only if the facility is solely or regularly used for military purposes.
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