KYIV, Ukraine — The fallout from the breach of a river dam along a front line of Russia’s war in Ukraine continued to wreak havoc on lives, livelihoods and the environment on Wednesday.

When the Kakhovka dam ruptured on Tuesday, it sent a torrent of water from Ukraine’s largest reservoir into streets and homes downstream on the Dnieper River where tens of thousands of people live — in the thick of a combat zone where shelling regularly takes place.

It’s not clear what caused the breach: the structure had already been damaged in the war.

Ukraine’s government, which controls the river’s western bank and the city of Kherson, has accused Russian forces of blowing up the facility.

Officials in Russia, which controls the eastern bank for about the last 185 miles before the river reaches the Black Sea, have blamed Ukrainian military strikes.

What Are the Latest Developments?

Authorities and rescue workers on both sides stepped up efforts Wednesday to pull beleaguered residents to higher and drier ground.

Volunteers in the city of Kherson buzzed around in inflatable motor boats to ferry people to safety or gather belongings left behind a day before.

Around 3,000 people were evacuated from both sides of the river, and water levels were continuing to rise, officials said.

Oleksandr Prokudin, head of the Kherson regional administration, said some 1,700 people had been evacuated in Ukraine-controlled areas by early afternoon on Wednesday. Hundreds of calls for help were still pouring into a government hotline, he said. The area has a population of about 42,000.

On the Russia-controlled bank, Moscow-appointed regional governor Vladimir Saldo said that 22,000 to 40,000 people remained in flooded areas. His deputy, Tatyana Kuzmich, said 1,274 people had been evacuated, and that the emergency response would last at least 10 days.

The head of the U.N.’s International Atomic Energy Agency, Rafael Mariano Grossi, tweeted about “concerning developments” in the wake of the dam breach. He said he would travel next week to the Zaporizhzhia nuclear power plant, which sits upstream on the edge of the reservoir.

Water from the river is used for cooling at the nuclear plant — Europe’s largest — but officials have said the dam breach poses no immediate risk to its safety.

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Who and What Remains at Risk?

The office of Ukraine’s general prosecutor said water levels downstream from the dam rose as much as 39 feet above normal levels, causing flooding in more than two dozen villages and towns in liberated areas.

Ukrainian President Volodymyr Zelenskyy wrote on Telegram that hundreds of thousands of people were without normal access to drinking water. Evacuation efforts in occupied areas had “completely failed,” he wrote, and Kyiv would appeal for international support.

Experts warned about the possibility of an environmental disaster for wildlife and ecosystems. Some of the biggest minefields in Ukraine were inundated, raising the prospect that the explosives could be moved around.

Ukrainian authorities urged locals to drink only bottled water and avoid eating fish from the river, among other warnings.

Why Is the Dam Important?

Operational since the mid-1950s under the Soviet Union, the dam and its associated hydroelectric power station are located about 70 kilometers (44 miles) east of the city of Kherson, and help bring electricity, irrigation, and drinking water to a wide swath of southern Ukraine.

Water in the reservoir is also channeled through a long canal that stretches to the Crimean Peninsula, which Russia illegally annexed nine years ago.

Ukraine’s vast agricultural heartland, which is partially fed by the Dnieper River, is crucial to worldwide supplies of grain, sunflower oil, and other foodstuffs.