Blasts at a Soviet-era dam in the Russian controlled part of southern Ukraine on Tuesday unleashed floodwaters across the war zone, according to both Ukrainian and Russian forces who blamed each other for blowing-up the dam.

KHERSON, Ukraine — A major dam in southern Ukraine collapsed Tuesday, flooding villages, endangering crops and threatening drinking water supplies as both sides in the war scrambled to evacuate residents and blamed each other for the destruction.

Ukraine accused Russian forces of blowing up the Kakhovka dam and hydroelectric power station, which sits on the Dnieper River in an area that Moscow has controlled for more than a year. Russian officials blamed Ukrainian bombardment in the contested area, where the river separates the two sides.

A satellite image shows an overview of the Kakhovka dam in southern Ukraine, where officials have accused Russian forces of blowing up the major dam and hydroelectric power station.  

Russian and Ukrainian officials used terms like “ecological disaster” and “terrorist act” to describe the torrent of water gushing through the broken dam and beginning to empty an upstream reservoir that is one of the world's largest.

Ukrainian President Volodymyr Zelenskyy called it “the largest man-made environmental disaster in Europe in decades.” U.N. Secretary-General Antonio Guterres, ahead of an emergency Security Council meeting, called it “another devastating consequence of the Russian invasion of Ukraine.”

The environmental and humanitarian consequences quickly became clear as homes, streets and businesses flooded downstream and emergency crews began evacuations. Officials monitored water for cooling systems at the Zaporizhzhia nuclear plant, and authorities expressed concern about drinking water supplies in both Ukrainian- and Russian-controlled areas.

A local resident makes her way through a flooded road  Tuesday in Kherson, Ukraine, after the walls of the Kakhovka dam collapsed overnight.

In the downstream city of Kherson, angry residents cursed as they tried to preserve their pets and belongings. A woman who gave her name only as Tetyana waded through thigh-deep water to reach her flooded house and rescue her dogs. They were standing on any dry surface they could find but one pregnant dog was missing. “It’s a nightmare,” she kept repeating.

Both Russian and Ukrainian authorities brought in trains and buses to move residents to safety. About 25,000 people in Russian-controlled areas and 17,000 in Ukrainian-held territory should be evacuated, Ukraine’s deputy chief prosecutor Viktoriia Lytvynova said on Ukrainian television. Neither side reported any deaths or injuries.

A satellite photo Tuesday morning showed more than 1,900 feet missing from the wall of the 1950s-era dam.

The dam break, long feared by both sides, added a stunning new dimension to Russia’s war, now in its 16th month. Ukrainian forces were widely seen to be moving forward with a long-anticipated counteroffensive in patches along more than 621 miles of front line in the east and south.

It was not immediately clear why either side might destroy the dam, and its collapse might have resulted from gradual degradation. Both Russian-controlled and Ukrainian-held lands were at risk.

Russian Defense Minister Sergei Shoigu charged that Ukraine destroyed the dam to prevent potential Russian attacks in the Kherson region after what he alleged was a failed Ukrainian counteroffensive. He claimed Ukraine lost 3,715 troops and 52 tanks since Sunday, and — in a rare acknowledgment of Russia’s own losses — said 71 Russian troops were killed and 210 wounded. Ukraine followed its standard practice of not commenting on its casualties.

Zelenskyy told reporters his government had information about Russia mining the dam last year, so “there may come a moment when an explosion occurs.” Other Ukrainian officials alleged Russia blew up the dam to hinder Kyiv's counteroffensive, though observers note that crossing the broad Dnieper would be extremely challenging. Other sectors of the front line are more likely avenues of attack, analysts say.

Nigel Gould-Davies, a senior fellow for Russia and Eurasia at the International Institute for Strategic Studies, said the alleged Russian destruction of the dam is “a profoundly defensive measure" showing "the lack of confidence in Russia’s longer-term prospects” in the war.

Experts previously said the dam was in disrepair, which also could have led to the breach. David Helms, a retired American scientist who has monitored the reservoir since the war began, said in an email it wasn’t clear if the damage was deliberate or simple neglect from Russian forces occupying the facility. He noted a Russian history of attacking dams.

Authorities, experts and residents were concerned for months about water flowing through — and over — the Kakhovka dam. After heavy rains and snowmelt last month, water levels rose beyond normal, flooding nearby villages. Satellite images showed water washing over damaged sluice gates.

Zelenskyy alleged Russian forces set off a blast inside the dam structure and said about 80 settlements were in danger.

Kremlin spokesman Dmitry Peskov called it “a deliberate act of sabotage by the Ukrainian side" aimed at cutting water to Crimea.

White House National Security Council spokesman John Kirby said the U.S. “cannot say conclusively what happened” and declined to say what impact it might have on Ukraine’s counteroffensive.

Both sides warned of a looming environmental disaster from polluted waters partly caused by oil leaking from the dam's machinery and farmland deprived of irrigation. Ukraine’s Presidential Office said some 150 metric tons of oil escaped from the dam machinery and another 300 metric tons could still leak.

The World Data Center for Geoinformatics and Sustainable Development, a Ukrainian nongovernmental organization, estimated nearly 100 villages and towns will be flooded.

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