In February 1945, towards the end of the second world war, a German V2 rocket struck Walthamstow Marshes in east London. The explosion tore a crater into the marshland. Left untouched, it slowly filled with water, sediment … and life. Today, this wartime scar has become a thriving pond.

“It’s small but it really punches above its weight,” says Luke Boyle, a ranger for the Lee Valley Regional Park Authority, as he kneels at the edge to examine aquatic plants sprouting their early spring shoots. “We can’t manage the hydrology here, so it is actually a vital part of the ecosystem – it supports a range of plants, insects and amphibians, more than you might expect,” he says.

Walthamstow’s Bomb Crater Pond lies within a fenced-off section of the marshes, protected as part of a site of special scientific interest. Its clear waters provide a year-round refuge for wildlife in an otherwise highly managed urban landscape. More than a million people visit Walthamstow Marshes each year, most unaware that the modest pond near the perimeter fence began its existence due to an instrument of destruction.

“It’s like an engine room for the marshes,” Boyle says. “Despite its size, it supports the wider ecosystem around it.”

Unlike most wetlands, there are no sluice gates here, no managed hydrology – the pond’s natural depth means it holds water all year round, reliable and clean. The cattle drink from it too, and their hooves disturb the ground around the margins, creating a patchwork of habitats that allow different species to take hold.

“In winter, you get snipe and lapwing out on the wetlands,” Boyle says, scanning the margins of the pond. “Then, by late spring, this becomes a breeding ground: newts and grass snakes. The dragonflies and mayflies come, butterflies along the edges.” Frogs and herons are regulars. “Last year was good nationally for butterflies,” he adds. “But, here, it’s like that every year.”

One species is creeping marshwort, among Britain’s rarest aquatic plants, recorded at only two sites in the UK. It is too early in the season to see it but Boyle knows it is there, somewhere beneath the surface, waiting. “We watch that carefully,” he says. “It’s about keeping the balance between open water and the vegetation that wants to take over.” Under a countryside stewardship agreement overseen by Natural England, he is required to maintain at least 80% open water, pulling out reedmace by hand when it encroaches.

It is, he adds, his favourite spot on the marsh. As he speaks, the Stansted Express flashes past on the elevated line beyond the fence. A grey heron circles above as if signalling it would like to land.

The power of small ponds

Small ponds have been one of ecology’s most underestimated assets. “Historically, because they are small, ponds have been dismissed as insignificant,” says Prof Jeremy Biggs, CEO of Freshwater Habitats Trust. “In fact, the evidence shows the opposite: across a landscape, they support a wider range of freshwater plants and animals – including more rare and protected species – than other freshwater habitats, such as big rivers or lakes.”

Part of the reason is counterintuitive. Bigger water bodies attract bigger problems. Rivers accumulate diffuse pollution from the land they drain. Lakes receive runoff from vast catchments. Ponds, by contrast, are small enough to avoid the systems that damage larger waters. Nobody routes a sewage outflow into a pond – it’s too small to dilute it.

“Ponds are powerful precisely because they are small,” Biggs says. “Many still hold clean water – something now increasingly rare in the wider countryside.” That, he adds, is why creating and protecting clean-water ponds is such an effective way to support freshwater biodiversity. They are also astonishingly varied – acidic or alkaline, shaded or open, grazed or undisturbed – and create a mosaic of conditions across any landscape that no single large water body could replicate.

“Darwin famously proposed that life began in a ‘warm little pond’, and freshwater species have spent millions of years evolving to colonise exactly these kinds of small, still waters,” says Biggs. “While it takes many decades or even centuries for most types of habitats to become established, wildlife arrives at new ponds almost immediately, and these small waters can become ecologically rich within just a few years.”

Evidence from bomb craters makes this vivid. Biggs says: “At Tommelen in Belgium, 144 ponds – many created unintentionally by second world war bombs – now form a nature reserve supporting seven amphibian species, including great crested newts and tree frogs.

“At Ashley Range in the New Forest, craters left by bouncing bomb tests, including one made by a 10,000kg bomb, have filled with water to create a network of ponds in heathland. These examples demonstrate how quickly ponds can become colonised. If the ponds are clean and in the right place, they can become rich habitats for a wide range of species.”

Every crater tells a different story

Some 1,500 miles (2,400km) east of Walthamstow, the ground tells a different story. Since Russia’s invasion of Ukraine in February 2022, the scale of destruction written into the landscape defies comprehension. Satellite imagery studies have identified more than 600,000 craters in just two southern regions (Mykolaiv and Kherson) alone. Across the country, researchers estimate the number now runs into millions.

The human cost has been devastating: tens of thousands killed, millions displaced, entire cities reduced to rubble. For Anastasiia Splodytel, a Ukrainian soil scientist who has worked across the country’s devastated regions, each crater marks a moment of violence.

What happens to the land afterwards is what she has spent years trying to understand. The answer, she says, is never simple. “It all depends on who is standing at the edge: their professional background, how they perceive what they see and a range of natural factors: soil type, the landscape-geochemical structure and the type of weapon used.”

A bomb does not simply tear a hole. The shock wave disrupts the layered structure of soil built up over centuries, deeply embeds metal fragments and recasts the microrelief. Some of the most extreme cases that Splodytel has encountered involve phosphorus munitions. White phosphorus burns at up to 2,760C – hot enough that fertile black soil turns into cracked stone. Ukraine’s chernozem, its famous black earth that is among the most productive agricultural soil on the planet, can be reduced in seconds to something inert. The thermal shock kills what lies beneath: the bacteria, fungi and microorganisms that drive fertility and regulate moisture.

Heavy metal contamination in individual craters does not always reach catastrophic levels, often rising only modestly above the natural background before stabilising. But Splodytel is careful about what reassurance that offers. “The main threat is not toxicity, but the loss of soil fertility – disruption of soil structure and reduction in microbial populations.”

Explosive compounds in the soil have barely been studied, and for communities living nearby, invisible contamination is easily underestimated. “It is precisely this underestimation that presents a significant threat,” she says.

Yet there is hope for even the most damaged soils Splodytel has examined. “I was pleasantly surprised by how quickly nature begins to heal itself without waiting for human intervention.” In shallower craters, she has observed accelerated pedogenesis – the rapid reformation of soil structure, new layers beginning to build almost before the dust has settled. Something, quietly, is trying to return.

For Bohdan Prots, a Ukrainian ecologist who has spent decades studying his country’s natural landscapes, there are few straightforward answers. His starting point is pragmatic. In up to 90 % of cases, the right course of action is simply to fill a crater with clean soil and return the land to use. “It is not as big a deal as people think when they talk about craters causing huge pollution. Not when you are looking at a single explosion.”

Scale changes everything. In the heavily bombarded zones of eastern Ukraine, where explosions have occurred every few metres, the cumulative effect is catastrophic, with entire forests reduced to bare earth, soil overturned to depths of several metres and the layered structure that took centuries to form pulverised beyond function.

And then there are the mines. “The problem is not really the crater,” Prots says. “The problem is unexploded devices.”

He describes a colleague’s father in the Kherson region who, on just half an acre of land, discovered 36 unexploded devices over three years, even after military deminers had certified the area clear multiple times. There is, he notes, a well-known rule: one year of war equals an average 10 years of demining. Ukraine, now four years in, already faces 40 years of that work ahead.

Yet he keeps coming back to something he has observed across a lifetime in the field. Growing up in western Ukraine, decades after the second world war, he found old bomb craters in the forest – depressions slowly silting over, but still functioning as miniature reservoirs. “They were already not as deep as before,” he recalls, but were “still a good resource for animals to drink and frogs to breed”.

He pauses over the observation for a moment. “Diversity of habitats, even created by war, leads to species diversity.”

Nature’s return is not always straightforward. The first species to arrive in damaged habitats are often pioneer or invasive ones, filling the vacuum before native plants and animals can re-establish. “People see green and think it is fine,” Prots says. “But green is not always beneficial.”

Each landscape must be read on its own terms, he says, whether that is wetland, forest, farmland or urban ground. Every crater carries a different story, depending on the soil, location, power of the explosion, intensity of the battle and whether clean water is present.

When asked about the postwar future – the tens of thousands of water-filled craters that will remain across Ukraine once the fighting ends – Prots’s answer is measured but not without hope.

“When it is in the forest,” he says, “it becomes a biodiversity hotspot. At the bottom of these explosions, which go three to eight metres deep, there will always be water in the end, even in very dry periods. It is like establishing a small wetland.”

He pauses. “And that is a place where animals are always eager to come.”

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