The destruction of Ukraine’s Kakhovka dam in June 2023 exposed lake bed sediment containing more than 90,000 tons of toxic heavy metals, setting off what researchers say is a toxic “time bomb.”
An early-morning blast on June 6, 2023, sent torrents of water surging through a breach in the mammoth Soviet-era structure, which had been in Russian hands since the year before, when it was seized early in the full-scale invasion of Ukraine. Ukrainian and Russian-controlled settlements along the Dnieper River were engulfed in floods, which forced mass evacuations and left dozens of people dead.
The rush of water out of one of Europe’s largest reservoirs submerged local flora and fauna, upending fragile ecosystems along the riverbank and in the Black Sea. Industrial pollutants, untreated sewage and waste from flooded factories and cities downstream were swept into the river, contaminating drinking water and arable soil. The rising water — which reached a depth of 15 feet in some areas — obscured marked minefields and swept explosives into new locations.
Russia and Ukraine have traded blame for the apparent attack: Wartime destruction of a dam would constitute a violation of the Geneva Conventions. Western intelligence assessments and several independent investigations have pointed to Russian responsibility.
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When the water receded, some Ukrainians returned to their homes in the floodplain. But a lingering threat remains, according to a study published Thursday in the journal Science. As newly exposed sediments in the Kakhovka reservoir lake bed erode, rain and seasonal floods risk sweeping tens of thousands of tons of toxic heavy metals embedded in the soil into the water supply, endangering local populations.
With the war ongoing, what happens to the site next remains an open question. The latest findings “should be considered when planning the future of this reservoir,” said Oleksandra Shumilova, one of the study’s authors.
For months after the flooding, researchers observed high concentrations of pollutants — including zinc, copper, arsenic, cobalt and oil products — at monitoring sites along the river. Nickel and zinc, which the researchers found in high quantities in the reservoir, are used in protective coating for metallic parts — and are toxic to humans in large quantities. Exposure to nondegradable heavy metals can damage the brain, liver, immune system and heart, and lead to congenital disorders.
The presence of heavy metals in the reservoir stems from large industrial polluters and agricultural concerns along the Dnieper, upstream from the dam, including factories, mines and metallurgical plants. Manufacturing and metallurgy are among Ukraine’s biggest industries.
Previously, the heavy metals were absorbed into the sediment at a molecular level, which kept them from being released back into the reservoir. But now that the water has drained, Shumilova said, the contaminants risk being absorbed by vegetation and moved through the local food web. The paper recommends a major construction effort — two barriers, each nine miles long, to cordon off parts of the reservoir that repeatedly flood — to combat the spread of the heavy metals. But those efforts can’t begin safely until the war ends, the paper’s authors write. The area in question remains under Russian control.
Some flora has reestablished itself in the previously flooded areas and has overtaken newly bare parts of the reservoir. One set of photos of the Kakhovka reservoir in 2024 shared by the researchers shows the footprints of wild animals, tracking through sparse vegetation — a hopeful sign.
“From that perspective, the whole idea of rebuilding a hydropower plant is bad, because now it will be a new environmental impact that we want to avoid,” said Olexi Pasyuk, executive director of Ecoaction, an environmental advocacy group in Ukraine.
But even as the ecosystems around the dam reestablish themselves, risks remain involving invasive, aggressive or non-native flora and fauna overtaking the floodplain, the researchers warn.
The total cost of the damage and losses from the incident is estimated to be nearly $14 billion, according to a report prepared by the United Nations and the Ukrainian government that was published in October 2023. Meanwhile, the prospects for reconstruction and recovery efforts — particularly as fighting continues — seem poor.
“Environmental restoration or remediation that requires substantial human input is costly and time-consuming, and often a low priority following armed conflicts,” said Doug Weir, director of the U.K.-based Conflict and Environment Observatory, who called the destruction of the dam “the single most environmentally damaging incident” of the war in Ukraine so far. “Areas where there is a significant risk of further damage from hostilities will struggle to attract what few resources there are.”
For their ecological assessment of the impact of the flooding, the researchers modeled the flow of water after the explosions at the dam, cross-referencing it with photos, videos and satellite imagery of the flooding. In addition, they analyzed data gathered in the field, including water and soil samples and photos from the land surrounding the river.
In some areas, vegetation was torn out of the ground by surging floodwaters. Elsewhere, riverbeds were blanketed with silt, burying animal habitats. Small-rodent populations in the area were probably reduced by 20 to 30 percent, the researchers estimate — endangering, in turn, the predators that rely on them for food. Along other parts of the river, entire generations of fish and some species of small animals may have been wiped out.
The release of freshwater into the Black Sea, into which the Dnieper empties, “undoubtedly” impacted marine life, the researchers write.
“If more dams are targeted, the human toll and environmental damage could be cataclysmic,” the paper’s authors write. “Protection of dams in military zones should be a priority concern for international law given the potential of conflict-related breaches to produce large-scale and long-term environmental impacts.”
Ongoing hostilities have made recovery and reconstruction work virtually impossible. They have also personally impacted some of the scientists studying the environment in Ukraine. The Science article is dedicated to the memory of one of them: Lyudmila Shevtsova, a hydrobiologist killed in a missile attack in Kyiv. Though Shevtsova didn’t work directly on the new paper, her work, Shumilova said, contributed to the data that was used in the article.
Just as the ecosystems around the dam have slowly started to reestablish themselves, so too have Ukrainians returned to nearby homes and fields, despite the looming ecological risks.
“People were very fast to return to these abandoned areas,” Pasyuk said. He and Ecoaction made efforts to reach out to communities across Ukraine where people were returning to dangerous land. Pasyuk hoped to warn them about mines and polluted soil, and to convince them that the land should be preserved — or at least professionally demined. There was “little interest,” he said.
“It’s very difficult to expect that people would be concerned with the potential long-term impacts to the health in a situation when there is a question of their immediate survival,” he added.
War in Ukraine