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Scientists don’t usually wear bulletproof vests and combat gear. But that was the reality that Ukrainian ecologists Anna Kuzemko and Yakiv Didukh lived through during their research trip to the former Kakhovka Reservoir in October 2023.
Then, the shelling brought their mission to an abrupt end.
“One mine fell just about 200 meters from our cars,” Kuzemko remembers.
It was not the first violence this region had witnessed. Less than four months earlier, Russians had blown up the towering dam that had held 18 cubic kilometers of water at bay. The disaster swamped over 80 towns.
In the old lakebed, all that remained were cracked terraces of dried mud. The cracks ran over a foot deep, as if butcher’s knives had carved cursed hieroglyphics into the land. The reservoir had turned into a pit of 500,000 tons of rotting zebra and quagga mussels. The air reeked with the sharp, rancid odor of these decomposing shellfish.
Just 100 years ago, this landscape looked very different. The Great Meadow, as it was known then, was a vast floodplain forest. Muddy flatlands crisscrossed with flowing branches of the Dnipro River, the banks bristling with thick stands of reeds and bulrushes. These marshes were fed a rich diet of nutrient-rich silt through the regular flooding. One of the historic homes of the nomadic Scythian and Cossack civilizations, this region cradled ancient ruins alongside chittering bird nests and fish spawning areas.
That all changed with the rise of industrialization. In the 1950s, the Soviets flooded the area, an act that some believe was meant to erase the region’s rich archeological heritage and erode the Ukrainian identity. In its place, they launched a vast cascade of hydroelectric dams along the Dnipro. At 3 kilometers long, the Kakhovka Dam was the project’s crown jewel.
For the next seven decades, these dams powered homes and irrigated fields. However, trouble was quietly brewing beneath the surface. The dammed river, although quite wide, had become very shallow, which meant less water for farmers to adequately irrigate their fields.
Meanwhile, the reservoir had also accumulated a steady runoff of pollutants and heavy metals from nearby industrial sites. Though the water technically remained drinkable, contaminants had been settling in the mud below. “The mud deposits on the bottom accumulated a lot of chemicals during the 70 years of the reservoir’s existence,” Kuzemko says.
In the early morning hours of June 6, 2023, just as the willows near the reservoir were sprinkling their seeds into the wind, Russia blew up the Kakhovka Dam. The explosion unleashed 7.2 million Olympic-sized swimming pools’ worth of water into the Dnipro River. For four days, the surge swallowed everything in sight, obliterating more than 620 kilometers of land and flooding 80 towns.
The disaster destroyed chemical storage facilities, flushing machine oil and industrial chemicals into the surrounding area. These contaminants were everywhere: sewage, pesticides, fertilizers, abandoned mines, rocket fuel, and ammunition — even radioactive chemicals that likely be traced back to Chernobyl. Early sampling revealed that silt from floodwaters contained persistent organic pollutants, pesticides like DDT, radioactive cesium, polychlorinated biphenyls (PCBs), and heavy metals like lead, arsenic, and mercury. Thanks to the decades of contamination that had already been lurking at the bottom of the reservoir and the additional swamp of pollution, the river that had once nourished over a million people had become a foul-smelling chemical soup.
Three weeks after the disaster, Kuzemko’s team came back to the remnants of the reservoir to calculate the damage. But they found an unexpected surprise: green seedlings.
“It was a very interesting landscape like from another planet… all these mud deposits on the bottom were covered with very tiny, very small seedlings,” Kuzemko says. The willow seeds that had been released at the time of the disaster had taken root in the nutrient-rich soil.
When Kuzemko and her team returned in October 2023, the difference in the landscape was stark. Almost 350,000 acres of the endangered floodplain forest had returned, covering a third of the affected area. This forest consisted of nearly 70 species of higher vascular plants, including a surprisingly high proportion of perennial plants, both of which indicate the emergence of stable habitats.
The star plant, of course, was the willow. The emerging thickets were packed with 20 individual plants per square meter. Several of the saplings had shot up to 2 meters tall, indicating a rapid growth spurt of up to 2 centimeters per day in the previous months.
Despite what the scientists feared, relatively few of the plant species were invasive. Like the willow, most dispersed their seeds by wind, as that was the most successful reproduction mechanism given the region’s post-catastrophe condition.
Many of the more dangerous substances had settled down into the riverbed. This soil was unlikely to spread, but still capable of causing damage. Meanwhile, contamination from fertilizer and sewage remained alarmingly high. Researchers feared that pollutants may have leached into underground wells, potentially contaminating local food supplies. And the problem wouldn’t simply wash away: many of these chemicals can remain dissolved in water or stick to the sediments that now coat the flood zones.
The star of the show could be the secret to truly reclaiming this tortured landscape. Willows can help buffer the area from the effects of climate change by absorbing carbon dioxide and stabilizing local temperatures, precipitation, and humidity. But they have an even more special property.
“Willow trees can accumulate a lot of heavy metals and other contaminants,” Didukh says. Because water quickly evaporates from their leaves, willow plants end up sucking a lot of water and the chemicals that are dissolved in it. The plant has a unique ability to absorb oil, nitrogen, and phosphorus. It can hold onto heavy and toxic chemicals within its body and in the soil around its roots, where it nurtures microorganisms that can help it break down some of the peskier contaminants.
Since the destruction of the dam, many of the residents who used to live nearby have left, perhaps for good. The ones who stayed behind are struggling for water without the reservoir. Can the willows, known for their natural purification abilities, help?
Experiments performed in Canada and the UK have been successful in using willow thickets to treat sewage. According to one estimate, 9-12 trees can purify enough water for one person, which means such thickets can treat wastewater for up to 5,000 people. They can also be used to decontaminate soils that are too unsafe to build on, as seen in Montreal, where an abandoned industrial site was transformed by planting willow trees.
Willow groves are also much easier and cheaper to manage than standard water filtration methods. “It’s very important to create a favorable environment for people and to solve problems with drinking water first of all,” Kuzemko says.
Some scientists warn that willows and other plants may not survive long due to the area’s frequent droughts. But others are more optimistic, their hope fueled by the willows’ rapid growth even in contaminated soil.
This October, Didukh returned to the site. “Although the frontline was not far away and we could hear the military shooting down enemy drones, we were invisible in the tall thickets of willows,” he says.
He reported that the trees have reached heights of almost 5 meters (the approximate length of a suburban street light) and their trunks have thickened to the diameter of ping-pong balls. The thickets are beginning to thin out as a few strong trees outcompete the rest. This “is a normal process,” Didukh says, indicating that the thickets have entered the next stage of maturation.
Meanwhile, new thickets of black and white poplars — characteristic species found in floodplain forests — have also taken root, giving hope in the midst of scenes of death and destruction. Some more invasive species like horseweed, Canadian fleabane, and the false indigo bush, also have established a presence, but this is a common issue among forests along river corridors. They will simply become part of the new ecosystem, Didukh says.
The change in the landscape of the former Kakhovka reservoir and dam from its destruction in June 2023 to a landscape of thriving willows and poplars in May 2024.
The willow's role as a potential savior is quite fitting. In Slavic culture, these trees symbolize hearth and home and are seen as protectors against evil. Alongside the reemerging thickets, ancient artifacts like Scythian pots and Cossack fortresses have surfaced. Could these herald a rebirth of Ukrainian cultures and landscapes?
Kuzemko thinks that it’s possible for the area to return to its historical state before the Soviets built the reservoir. The thickets fit the criteria for rare habitats to be protected by the Bern Convention and EU Habitat Directive. There’s even international interest in a rewilding project, which would align with the European Union’s "Bringing Nature Back into Our Lives" program, aimed at restoring 25,000 kilometers of rivers to their natural state by 2030.
However, Ukrainian hydropower company Ukrhydroenergo wants to rebuild the dam, arguing that this would attract residents and allow the nearby nuclear power plant to reopen. Others advocate for a smaller, deeper reservoir, which would allow the burgeoning ecosystem to remain.
“There is a big discussion between ecologists and hydrologists,” Didukh says. “For ecologists, it’s more important to save these habitats and ecosystems which are now starting to grow.”
“The new willow forests are seen as valuable for their ecological services,” Kuzemko says. “We are trying to show that nature also has [value]… nature can provide a lot of benefits for the population in all over Ukraine and also in this region.”
Kuzemko points out that these plans are not just about saving a unique ecosystem; they’re also about preventing further harm. Rebuilding the dam would mean dismantling these thickets that prevent decades' worth of contaminants from spreading far and wide.
“If this forest will be flooded, all these chemicals will be released into the water,” Kuzemko warns. “It will be a new ecological catastrophe.”
