A critical dam on the Dnipro River in southern Ukraine broke overnight on Tuesday, endangering tens of thousands of people who live downstream. It was not clear what caused the breach. Ukraine blamed Russia, saying that there had been an explosion in an engine room. Russia said that Ukrainian forces had carried out sabotage.
Ukrainian officials began evacuating people in the Kherson region on Tuesday as huge volumes of water gushed from the dam’s reservoir. Floodwaters were expected to rise through the night and peak on Wednesday morning, the head of Ukrhydroenergo, a state-owned hydropower company, said in an interview.
The U.N. secretary general, António Guterres, decried the destruction of the Kakhovka hydroelectric dam, calling it a “monumental humanitarian, economic and ecological catastrophe” and “yet another example of the horrific price of war on people.”
The dam is near the front line of the war.
Videos of the dam, in the town of Nova Kakhovka, reviewed by The New York Times do not reveal what caused the destruction. But they do show water flowing freely through the dam, indicating severe damage.
A day before the disaster, American and Russian officials said a planned Ukrainian counteroffensive appeared to have begun east of the Dnipro River in the Donetsk region. The flooding could divert both sides’ attention and resources from that counteroffensive.
Located near the front line of the war in the southern Kherson region, the dam and nearby infrastructure have been damaged by shelling throughout the war. The area including the dam and the adjacent hydroelectric plant has been occupied by Russian forces since last year. The Ukrainians now say the power plant cannot be restored.
Engineering and munitions experts said that an internal explosion was the most likely cause of the destruction.
Russia and Ukraine traded blame.
On Tuesday, Russia and Ukraine blamed each other for the destruction, without offering evidence.
President Volodymyr Zelensky of Ukraine blamed “Russian terrorists,” while the Kremlin’s spokesman, Dmitri S. Peskov, blamed Ukrainian forces, describing what happened as sabotage.
“They decided that now, in this way, they will be able to stop the counteroffensive of Ukrainian forces,” Natalia Humeniuk, a spokeswoman for Ukraine’s southern command, told Radio Svoboda on Tuesday.
Sergei K. Shoigu, Russia’s defense minister, accused Ukraine of destroying the dam, saying Kyiv wanted to move forces and equipment defending Kherson to other parts of the front to help with its counteroffensive.
Security of the dam, a vital source of water and power, has been a continuing concern during the war, with both sides accusing the other of plotting to destroy it.
John F. Kirby, a spokesman for the National Security Council, said that the United States had been monitoring the effects of the destruction of the Kakhovka dam but that he could not confirm news reports that Russia was responsible.
Thousands of people are at risk.
Communities along the waterway are at risk of being flooded and washed away. More than 40,000 people could be in the path of flooding on both the Russian- and Ukrainian-controlled sides of the river, according to the deputy prosecutor general of Ukraine.
In telephone interviews arranged by a group distributing humanitarian aid in Antonivka, residents described how they had watched as rising waters crept from house to house. They kept their distance from the river bank, where Russian snipers on the opposite side have in the past fired at residents, they said.
The eastern bank of the river, south of the dam, is controlled by Russian forces.
The damage threatens to disrupt vital services provided by the dam’s reservoir. It will cause a severe shortage of drinking water in the Dnipro, Zaporizhzhia and Kherson regions, said Ihor Syrota, the hydropower company chief.
Flooding could also wash mines from their original positions into previously safe areas, posing a fatal risk to civilians returning to their homes. Russian officials say the destruction could pose problems for a canal supplying water to Crimea.
It also provides water for the cooling of reactors and spent fuel at the nearby Zaporizhzhia Nuclear Power Plant, but Ukrainian officials and the U.N.’s nuclear watchdog said Tuesday that the facility was not at immediate risk of meltdown as a result of the damage to the dam.
Towns are submerged, with waters still rising.
Towns continued to disappear under the water flowing from the reservoir early Wednesday, forcing more residents to evacuate. In Nova Kakhovka, where the dam is, the city hall and Palace of Culture were inundated.
Floodwaters swept even areas miles downriver. Residents in one village could be seen wading through their front yards, rescuing pets and belongings. Roads were submerged, putting people trying to escape at risk of being stranded.
The magnitude of the flooding’s impact is difficult to gauge as waters are still rising. Reliable information is hard to come by, especially from the Russian-held areas east of the Dnipro River. Shelling has continued as residents escape their flooded homes.
