We need to leap over the beaver dam.

We need to leap over the beaver dam.

Although most of my time is spent below the surface with fish, I’m a general naturalist at heart (albeit with a bias towards freshwater wildlife!) One creature I’ve always wanted to see is the beaver, though on my travels filming freshwater fish I often meet people who are in two minds about the return of these toothy rodents.

There is something magical about seeing a beaver dam. The almost cartoon-esque trees they whittle down, the tell-tale clues dotted about the catchment. Though I’m yet to see one in the flesh, I can certainly see the benefits they could have to Britain’s fish. 

Freshwater fish in Britain face a whole host of problems. From tonnes of raw sewage being discharged into our rivers each day, habitat degradation, invasive species and all the other usual culprits that threaten British wildlife. It’s perhaps no surprise then, that many anglers are cautious of beavers – wary of disturbing an already pressured ecosystem. 

Species like salmon need to reach their natal river. Their journey arduous and well known – travelling from as far as Greenland back to British rivers and moving upstream to spawn. They face many obstacles from weirs, to predators, pollution and disease. 

One of the main concerns of many anglers is that beaver dams pose a physical ‘block’ on rivers and fish migration – preventing this most ancient and fundamental movement. I once had these thoughts. But, as I spent more time learning about beavers and speaking with those experienced in their presence, I was surprised and pleased to find out that their iconic ‘engineering’  – although conspicuous and impactful – cultivates braided meandering rivers, with clean and extensive spawning gravels for fish. Creating, instead of preventing. Surely we have played a part in disturbing migratory fish movement, as rivers have become straightened, canalised and dredged?

Compelling evidence from trials such as the River Otter Beaver Trial suggests that young fish grow faster and return to sea healthier if they live in beaver ponds. The fittest and strongest fish will get past the dams ensuring that the best genes are passed on in the prime spawning areas. If beaver dams are left to establish alongside appropriate management techniques, the subsequent flooding will create side-channels around the dam, such that if the dam is unsurpassable, there are options for the fish to navigate the bypass and continue upstream.  

Many invertebrates also live in the dams, as its huge mud and wood structure offers plenty of food for growing fish fry. One of the significant issues in Britain is that our rivers are increasingly devoid of woody debris. Lamprey, for example, need large areas of mud and silt to filter feed when young – something all three species found in the UK do. Mayflies, a hugely important part of the riverside ecosystem and one of the first riparian colonisers, also depend on silt and mud to dig into – so beaver dams create a stable and perfect home for them. In turn, the bumper hatches of mayflies feed the surrounding birds when they are rearing young. With the trees felled and beaver dams built, these are five star hotels for the small fish and invertebrates. As well as effective hideouts from predation, beaver dams also create a shelter for many young fish when the winter floods hit, which often wash many juvenile fish out to sea that are unable to escape the current. 

As someone with a lifelong passion for what lurks beneath the waterline, I’ve quickly come to realise that the solution to ‘the beaver problem’ is education. It’s a simple case of accepting that beavers and migratory fish have co-existed for millennia – their biology, behaviour and life-history strategies showcasing that beavers and fish can cohabit a catchment and mutually benefit. We need to allow rivers to reconnect with the floodplain, so that beaver dams are less likely to affect beaver passage. Rivers need space. And it’s time we let nature have a bit more of a say in the matter.*