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LONDON — Until two years ago, West London’s Greenford Tube station used to flood whenever it rained heavily. The train tracks are aboveground, but the ticket office would often get inundated. Sandbags still line the corridor.

But in October 2023, a new family moved in nearby, determined to halt the water. The family members built their house from scratch with local wood and kept odd hours, sleeping all day and working only at dawn and dusk. They even put their young children to work.

The new neighbors were beavers.

The beavers are part of an unlikely effort to bring back a vanished species and help Britain adapt to a very modern problem: climate change.

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Britain is famous for drizzle, but climate change is making rainfall heavier and more erratic. Places that didn’t used to flood are now waterlogged. So scientists have enlisted some of the animal kingdom’s best flood engineers — beavers — to help.

In West London, conservationists got a government license to resettle a family of five beavers in a 20-acre urban park near the Greenford Tube station. It used to be a golf course, with a creek running through it. Within weeks, the beavers dammed up the creek, creating a pond that holds water and stops it from spilling into the city. They also diverted the creek’s flow into smaller tributaries, creating a wetland that better absorbs heavy rainfall — mitigating the risk of flooding downstream.

“They effectively turned this site into a giant sponge that can take heavy rainfall and slowly release water back into the landscape, creating a lot more resilience for flooding,” explains Sean McCormack, a local veterinarian who started the Ealing Beaver Project, named for the London borough of Ealing, where it’s located.

Not only has the local Tube station stopped flooding, but the beavers have also coaxed back other species.

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“By felling trees, they’ve also opened up the canopy, and we’ve seen an abundance of biodiversity,” McCormack says.

Freshwater shrimp have appeared in the creek, he says, plus eight new species of birds, two types of bats and rare brown hairstreak butterflies, which lay their eggs on blackthorn branches nibbled by beavers.

The beavers have also allowed the city to scrap expensive plans to dig a reservoir and levee.

“We said the beavers can do it for a fraction of the cost, certainly more sustainably,” McCormack says.

Now, joggers and teenagers stop to gawk at the beavers in action. There are guided walks and beaver safaris.

On a recent spring evening, a reddish-brown adult scampered in and out of the water, chomping on a felled willow tree. Eurasian beavers can weigh up to 65 pounds; this one was the size of a fat golden retriever.

The Ealing Beaver Project is one of dozens of sites across Britain where land managers are using beavers to restore wetlands and tame flooding.

But first, they had to bring them back from extinction.

Reintroducing beavers to Britain for the first time in centuries

In Britain, humans hunted beavers to extinction more than 400 years ago. By the early 20th century, only about 1,200 native beavers were left in Europe and northern Asia, surviving in parts of Norway, France, Germany, Belarus, Ukraine, Russia, Mongolia and China. Sweden reintroduced them in the 1920s, and other countries followed — part of a broader effort to restore native species.

By studying fossils, scientists determined that today’s Norwegian beavers are genetically most similar to the beavers that lived in Britain centuries ago. So in 2009, wildlife officials relocated two Norwegian beavers to Knapdale Forest, a temperate rainforest in western Scotland. That pair, named Millie and Bjornar, became the Adam and Eve of the modern-day British beaver population. The Scottish forestry department calls them the “original beaver power couple.”

“We became kind of attached to Millie and Bjornar,” says Pete Creech, a forest ranger who remembers when they arrived, scrambling out of crates and splashing into a loch. He recalls their enthusiasm: “Lots of squeaking!”

Creech set up hidden cameras to capture their crepuscular (dawn and dusk) movements. Within weeks, the beavers dammed up a tiny river, creating an enormous lagoon where swans now nest.

While the United Kingdom overall is getting wetter, some areas — including parts of Scotland — are getting drier, even seeing a growing threat of wildfires. Beavers ensure this rainforest stays wet and, thus, abundant. That’s especially important at a time when wetlands are disappearing, with many drained for development.

“Wetlands are one of the most biodiverse habitats in the world,” Creech notes. “The U.K. has lost over 95% of its wetlands, and now we’re frantically trying to put them back.”

Not everyone thinks rodents are the best way to do that, though.

Conflict with farmers

Unlike in London, where they’re enclosed in urban parks, beavers in Scotland went forth and multiplied, spreading onto private land. Their numbers have been boosted by beaver bombers — renegade wildlife enthusiasts who’ve released unlicensed beavers into areas where they might not be welcome.

“As the beaver population has expanded, we’ve seen more [farmers] getting concerned,” says Kate Maitland, a regional representative for Scotland’s National Farmers Union.

Beavers can dam up irrigation channels, flooding crops.

“It’s quite devastating to see acres and acres of your land sitting underwater,” Maitland says.

They can also fell centuries-old trees and collapse riverbanks, exacerbating erosion. Maitland, a farmer’s daughter, says she once got the full length of her leg stuck in a beaver burrow while walking along the banks of a stream on her family’s land.

The Scottish government has set up a fund to rebuild riverbanks and other beaver damage, if repairs are in the public interest. That doesn’t typically cover damage to private land.

Some farmers shoot beavers, though they need a license to do so, since beavers are a protected species. It’s also illegal to disassemble beaver dams or lodges that are more than two weeks old. Instead, farmers are encouraged to call wildlife officials, who trap and relocate beavers. That’s where London’s beavers came from.

Other farmers have learned to like the new neighbors — and even celebrate them.

Learning to live with beavers

Tom Bowser is a fifth-generation farmer in central Scotland. He has empathy for his fellow farmers: “When you’re trying to grow food, the presence of a fat semiaquatic rodent who wants to raise water levels is understandably going to be unpopular!”

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Bowser’s farm is strewn with trees felled by beavers. Many of the tree trunks have been whittled into hourglass shapes by beavers’ sharp teeth. Some of them teeter, about to fall.

He finds it fascinating.

Bowser wraps young trees in chicken wire if he wants to protect them. (In London, officials painted trunks with sand, which gets stuck in beavers’ teeth.) But he has found that the benefits outweigh the costs.

A beaver dam has diverted floodwaters from his driveway, creating a pond lined with benches that’s frequented by tourists. He runs spring and summer beaver-watching tours that are especially popular with children, who previously knew beavers only from fairy tales.

“We get people from all around the world coming here now!” Bowser says. “Growing up here, you didn’t see any car you didn’t recognize.”

Beaver fever is spreading

The beaver buzz is catching. The animals have made comebacks in Italy, Portugal and the Ukrainian part of the Danube River delta. In the United States, the Methow Beaver Project releases them into fire-damaged areas of Washington state. In Idaho, NASA is helping track beavers’ work.

In Britain, beavers are especially popular with land managers who are short-staffed.

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South Norwood Country Park is a 125-acre nature reserve with only one employee. Volunteers do some of the ground maintenance. They even don waders to dredge streams once a year.

“That’s exactly the sort of work the beavers would do naturally,” says countryside warden Ian Glover. He has applied for a license and hopes to welcome beavers in 2028 or 2029.

Like Ealing, South Norwood is on London’s urban periphery. It’s famous for birds, with boxes for kestrels to nest in perched atop poplars. The park’s peak bird count — 177 species — goes back to 1935. But birds have been in decline across Europe.

Glover hopes beavers might help reverse that locally, by damming up streams and creating wetlands that attract more birds.

Beavers build dams and raise water levels in part to hide from predators, Glover notes. But most of their predators — including wolves and bears — have been extinct in Britain for centuries.

“Obviously they haven’t gotten the memo,” Glover laughs.

And these beavers have been so useful, nobody’s telling them.

Edited by Rachel Waldholz