The destruction of a large Ukrainian dam in 2023 triggered a “toxic timebomb” of environmental harm, a study has found.

Lakebed sediments holding 83,000 tonnes of heavy metals were exposed when the Kakhovka dam was blown up one year into Russia’s invasion, researchers found. 

Less than 1% of these “highly toxic” heavy metals – which include lead, cadmium and nickel – are likely to have been released when the reservoir drained, the scientists found. They said the remaining pollutants would leach into rivers as rains wore down the sediment, threatening human health in a region where river water is widely used to make up for shortages in municipal water supplies. 

The lead author, Oleksandra Shumilova, said the scale of the environmental impacts was comparable to the Chornobyl nuclear disaster.

“All these pollutants that were deposited on the bottom can accumulate in different organisms, pass through the food web, and spread from vegetation to animals to humans,” said Shumilova, a scientist at the Leibniz Institute of Freshwater Ecology and Inland Fisheries. “Its consequences can be compared to the effects of radiation.”

The researchers linked on-the-ground measurements with remote sensing data and hydrology models to map the environmental impacts of the dam’s destruction, which flooded the region and killed 84 people. They estimated water from the breach killed 20-30% of floodplain rodents, along with the entire juvenile fish stock. 

They said the reservoir released 9,000-17,000 tonnes of phytoplankton each day in the first week after the dam was blown up, driving an increase in water turbidity that led to the “probable loss” of 10,000 tonnes of macroinvertebrates.

The destruction of natural life detailed in the study appears to contrast with the striking images of wildlife that has returned to the reservoir since the dam burst. White willows and black poplars have reforested the land, and wild boars and other animals have taken over areas that people still avoid. Fish that have not been seen for decades, such as sturgeon and herring, have returned to the water.

The researchers expect that the area will reach a level of biodiversity equivalent to 80% of an undammed ecosystem within five years.

“It’s not recovery, it’s better to use a word such as re-establish,” said Shumilova. “It means that it will develop its own way, but not necessarily to the initial conditions.”

The Kakhovka dam, which was built in the 1950s on the Dnipro River, was destroyed on 6 June 2023 while under Russian occupation. Its reservoir supplied water to cool the Zaporizhzhia nuclear power plant and irrigate southern Ukraine.

Before and after Nova Kakhovka dam collapse in Ukraine – video

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Ukrainian ecologists have debated whether the dam should be rebuilt after the war – and how much land should be flooded if it is – with some arguing for the new ecosystem to be left alone as part of a growing movement to rewild human-disturbed areas. Shumilova said that the unresolved question of heavy metal contamination complicated this approach, because it was unclear whether the vegetation was enough to keep the exposed sediments in place.

“It’s still something that people have to investigate,” she said. “Presently, it’s difficult because of the war – it’s difficult for scientists to go there to take samples and conduct experiments.”

Shumilova, a Berlin-based researcher whose home town of Mykolaiv was cut off from water for a full month at the start of the war, said the study findings were relevant for peacetime removals of large dams, as well as for other wars between industrialised countries.

Water has repeatedly been used as a weapon of war in Ukraine, with attackers and defenders having blown up dams for military gain. Legal scholars say the destruction of the Kakhovka dam, which Ukraine blames on Russia, and which Russia disputes, could constitute an environmental war crime.

Shah Maruf, a law researcher at the East West University in Bangladesh who has published research on the legal consequences of the Kakhovka dam’s destruction, said the new findings “suggest that the damage is ‘widespread, long-term, and severe’, fulfilling one of the key requirements for an environmental war crime”.

But he added that the speed of the ecosystem’s recovery could affect the strength of the case. “If the recovery is faster – and if that was anticipated by the perpetrator while attacking – that may compromise the finding of ‘long-term’ damage in the context of environmental war crime.”

Last month, a separate study exploring the effects of the Kakhovka dam destruction on the Black Sea ecosystems observed some habitats and species replenishing, but found “significant habitat destruction, disturbances and pollutant damages remain”.

Carol Stepien, an ecologist at the Smithsonian Institution and co-author of the study, said Ukraine’s freshwater, estuarine and marine species “evolved under conditions of longtime flux”, exposing them to a range of temperatures, salinity levels and habitat qualities. This “may aid their resilience and recovery”, she added.

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 This article was amended on 17 March 2025 because an earlier version referred to Shah Maruf as a law researcher at the University of Dhaka; he has now moved to the East West University in Bangladesh.

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Ajit Niranjan

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