Walk along Zurich's Limmat riverbank and you might notice something odd: fresh wood chips scattered on the footpaths, tooth marks carved into tree trunks, and entire riverside willows reduced to stumps. But this isn't vandalism, it's the work of Zurich's newest residents with serious engineering ambitions: European beavers are reshaping the city's riverbanks, one tree at a time.
Their presence in Switzerland's largest city is a relatively recent phenomenon. After being completely eradicated from Switzerland's landscapes in the 19th century, the beaver is reclaiming not just rural areas, but also increasingly pushing into urban rivers and lakes2.
The beaver's comeback in Switzerland began in the 1950s through the efforts of passionate individuals. Anton Trösch, for instance, imported six beavers from Norway in 1968 and released them in a lake in Canton Thurgau (Figure 1). Since 1962, beavers have been protected under the Swiss Federal Hunting Act, and their population has grown steadily, from just 111 animals in 19781 to approximately 4'914 by 20222 (Figure 2).
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The return of the beaver to Switzerland was long seen as a rural success story. Yet today, with territories in rural areas becoming increasingly occupied, beavers are expanding into urban spaces as well. This shift brings both promise and friction. As ecosystem engineers, beavers can create biodiversity hotspots, retain stormwater, and recharge groundwater3, benefits that align well with urban sustainability goals4. But their engineering activities can also clash with city life: flooded footpaths, felled park trees3, and occasional confrontations with domestic animals reveal the tensions of coexistence.
Can beavers and people truly share the same spaces? And if so, how do we balance their ecological contributions against the disruptions they cause? To explore these questions, we spoke with Livia Moser from the Beaver Office of the Canton of Zurich, who monitors beaver activity across the southwestern part of the canton, including the city itself.
According to Moser, in spring 2025 there were six active beaver territories in the city of Zurich, home to around 20 animals in total. Three of these territories lie along the Limmat River5, the source of those gnawed trees near the Lettensteg and beyond.
Why Cities Need Beavers
The reappearance of the beaver in Zurich represents more than the return of a native species; it signifies a broader restoration of ecological processes within an urban context. As "ecosystem engineers," beavers modify their surroundings in unmatched ways that offer advantages for both the environment and the community.
Beaver Comes, Biodiversity Booms
Wherever beavers settle, biodiversity follows. By building dams and holding water back, beavers support a broader diversity of microhabitat than the previously uniform stream systems. As Livia Moser pointed out, human-led habitat restoration rarely achieves the scale of change that beavers produce naturally and continuously. Interestingly, even when the beavers move on from one location, biodiversity still increases.
"We often try to achieve such effects through upgrading, but often not to the extent that the beaver does."
Water Retention and Climate Resilience
In a warming climate, where Zurich increasingly faces dry and hot summers, beavers act as natural water managers. Their dams slow down streamflow, keeping more water in the landscape and allowing soils to remain moist for longer. These wetter areas become crucial refuges for aquatic species that might otherwise struggle to survive seasonal droughts. The cooling effect of retained water also contributes to microclimate stabilization - an invaluable service in an urban setting.
Chew, Chew, Change the Landscape
By feeding on woody vegetation such as blackberry bushes, beavers open up dense areas and allow grasses and meadow plants to flourish. This in turn provides food and habitat for a variety of insects. Their influence creates dynamic, ever-changing environments that benefit many species - not just themselves.
Nature's Unexpected Teachers
In a city like Zurich, the presence of beavers has another unexpected advantage: educational impact. Residents, joggers and passersby who encounter gnawed trees or the sight of a beaver family at dusk are prompted to engage with urban nature more deeply. Even a fallen tree on a footpath becomes a moment of environmental learning.
"It is important to realize that there is something else besides humans."
Common name: Eurasian beaver
Scientific name: Castor fiber
Family: Castoridae
Length: 73–135 cm (excluding tail)
Weight: 13–35 kg
Habitat: Rivers, lakes, and wetlands
Diet: Bark, twigs, leaves, and aquatic plants
Notable traits: Beavers are skilled builders that create dams and lodges. By shaping waterways and opening up dense vegetation, they act as key ecosystem engineers and promote biodiversity.
Did you know? Beavers have transparent eyelids that allow them to see underwater while swimming and diving.
The Challenges of Coexistence
While the return of beavers to Zurich brings valuable ecological benefits, it also introduces several challenges that require careful management. Recognizing these risks is essential to develop strategies that support coexistence while protecting urban infrastructure and public safety.
Localised Flooding
Although the main rivers in Zurich generally provide sufficient water depth for beaver lodges without the need for dam-building, localised flooding can still occur. Beaver activity can change water flow in smaller streams or side channels, which may affect drainage and needs to be monitored.
Impact on Infrastructure
Beaver lodges and underground tunnels can destabilise riverbanks and footpaths if left unchecked. In some cases, tunnels weaken the ground beneath pathways, increasing the risk of collapse. Technical interventions, such as reinforcement of paths or controlled water flow measures, are sometimes necessary to maintain public safety.
Felled Trees
Tree felling for building material and food, is a natural part of beaver behaviour. In Zurich, this can affect old or valuable trees along rivers, potentially altering the urban landscape or even endanger humans and infrastructure when a tree falls. Targeted protection measures, like tree guards, may be needed to preserve particularly important trees.
"In urban areas, older trees, which were gnawed on by beavers could fall over and pose a danger."
Clashes with Domestic Animals
Beavers are generally shy and avoid humans and pets. However, in rare cases – particularly when cornered or defending their young – they may react aggressively towards dogs. Such incidents are uncommon but have happened in Zurich in the past and illustrate the importance of maintaining respectful distances and keeping dogs on a leash in sensitive areas.
"There have been isolated cases where beavers have attacked dogs, but these are very few indeed."
Population Growth
If the local beaver population grows significantly in the future, territorial stress can increase, potentially leading to competition for suitable habitat. This can require careful monitoring to ensure the urban ecosystem can support the number of beavers present without causing conflicts as beavers are known to be aggressive against other, unfamiliar beavers in their territory.
"If the beaver population continues to grow, density stress could occur."
Is Zurich Ready for the Beaver Fever?
The re-establishment of beavers within Zurich's urban landscape demonstrates that cities can accommodate ecosystem engineers when their impacts are understood and managed. The ecological benefits habitat diversity, water retention and vegetation structuring Alien with urban sustainability goals and contribute to climate resilience.
But perhaps the beaver's most unexpected contribution is educational. As Livia Moser observes, beavers provide “free education” simply by existing. Residents who encounter gnawed trees or glimpse a beaver family at dusk are suddenly confronted with questions they might otherwise avoid: How much wildness are we willing to accommodate? What disruptions are acceptable for richer ecosystems? In Oerlikon, a school seized this opportunity, integrating beaver activity into lessons because the animals were suddenly unavoidable neighbours. Whether voluntary or involuntary, this engagement with urban nature marks a shift in how residents understand their environment.
With appropriate management—tree protection, water monitoring, public education—the practical challenges of coexistence are solvable. The deeper challenge is conceptual: accepting that Zurich's waterways aren't fully ours to control. Beavers don't ask permission or follow regulations. They reshape their habitat according to an ecological logic that predates cities by millions of years.
The question is not whether Zurich can technically accommodate beavers. It is whether residents are ready to accept what their presence implies: that nature, given the chance, has its own plans for urban waterways.
"After all, Zurich is a city by the water and naturally the beaver belongs to this ecosystem."
Authors: Amélie Chatelain, Damian Glauser, Jari Kern, Luis Gentner, Pascal Soland
References
- Stocker G. Biber (Castor fiber L.) in der Schweiz. Birmensdorf: Eidgenössische Anstalt für das forstliche Versuchswesen; 1985.
- Angst C, Auberson C, Nienhuis C. Biberbestandeserhebung 2022 in der Schweiz und in Liechtenstein. Neuenburg: Info Fauna - Biberfachstelle. 2023.
- Bailey DR, Dittbrenner BJ, Yocom KP. Reintegrating the North American beaver (Castor canadensis) in the urban landscape. WIREs Water, 6(1). 2019.
- Stadt Zürich. Fachplanung Stadtnatur: Planungsgrundlage für das Netzwerk ökologisch wertvoller Lebensräume. 2024.
- Nienhuis C, Elmiger C, Schnyder J, Schell C and Hofstetter A. Der Biber im Kanton Zürich. Bestand und Verbreitung im Winter 2025. Fischerei- und Jagdverwaltung des Kanton Zürich. 2025.
- Holden J. Castor Fiber. Animal Diversity Web. 2009 (Accessed December 15, 2025).
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