Cheap but invasive: Are beavers the key to Ireland’s flooding woes?

The case for Ireland following its neighbours in introducing ‘the quintessential ecosystem engineer’ to our rivers

If I told you there was a solution to the issues of flooding, drought, water quality, biodiversity loss and even fires that required no major infrastructure, lengthy planning permissions or costly technology, minimal maintenance and was cheap and easy to implement, you would surely want to know more.

If I told you this solution was already being used across Europe and North America and that the science was already there to demonstrate its impact, perhaps you’d be scratching your head wondering why we were not simply getting on with it!

The solution I’m referring to is beavers. The charismatic, Jack Russell-sized rodents are what a 2020 study from the University of Exeter in the UK described as “the quintessential ecosystem engineer”. The researchers described how beavers’ dams hold back water during peak flood and maintain water flows during droughts, and how they increase the biodiversity of river corridors by selectively felling trees, thereby increasing the volume of dead wood and opening shaded areas to light, “providing rich habitat for insects, birds, bats and amphibians”.

The dams trap sediment, thereby storing carbon and enhancing downstream habitat for spawning fish, particularly salmon and trout; and they can even help to restore the natural sinuosity to rivers, many of which have been artificially straightened and deepened. The paper concluded that beavers “may have a substantial role to play in the renaturalisation of river systems”.


Féidhlim Harty, director of FH Wetland Systems and someone who has been working on “nature-based solutions” to water management in Ireland for nearly 30 years, agrees and thinks that “absolutely” beavers should be introduced. He has been experimenting with “beaver dam analogues”; basically a human attempt to build a beaver dam with logs and dead brash and found them effective at holding back water, restraining and filtering the flow before it moves on downstream. But the advantages are many.

But there is a catch. Beavers are not proven to have ever been in Ireland. Therefore, any release of the rodents into the wild would be an ‘introduction’ as opposed to a ‘reintroduction’

“They’ve got the advantage of providing fire breaks with the landscape, also they’ve been shown to improve biodiversity, they bring back wetland habitats which are sorely needed... they improve the quality of fish stocks, they improve the hydrodynamics – reducing flooding and reducing droughts – they can help to recharge groundwater,” he adds.

They would “work to undo the damage caused by the Arterial Drainage Act”, referring to the legislation, dating to 1945, that requires the Office of Public Works to continually dredge and drain over 11,500km of river channel, something that leads to ecological degradation and increased risk of downstream flooding. He added that the Act “should be changed radically, if not scrapped”.

But there is a catch. Beavers are not proven to have ever been in Ireland. Therefore, any release of the rodents into the wild would be an “introduction” as opposed to a “reintroduction”. Once hunted for their fur and castoreum (a scented secretion believed to have had medicinal properties), beavers have made an astonishing comeback across the European Continent while since 2009 a number of reintroductions have been successful in Scotland and England – most recently to Ealing in West London.

While some ecologists in Ireland think that beavers must have made it to Ireland (given their ability to swim and the abundance of perfect habitat for them here in the past) the fact remains that there is no evidence, such as bone fragments or gnawed logs, to back this up.

Mary Bourke, assistant professor of geography at Trinity College Dublin, who is researching nature-based solutions to flooding in Ireland, agrees that “the scientific evidence is there to support the effectiveness of beavers in cleaning waterways and reducing peak flooding. But until we find bones we shouldn’t be thinking of introducing them”.

Having lived in Australia, she has seen the damage that invasive species can do. She also notes that we don’t have enough trees to support beavers. “We have very limited riparian [riverside] forest and so there isn’t the standing wood there to allow beavers make their dams.”

Indeed, trees and vegetation have been zealously cleared from riverbanks across the country in the belief that they cause flooding. Many of our rivers have been denuded of any kind of vegetation, as well as being straightened and deepened under government-funded drainage schemes.

“I would not have beavers on my list. There is so much more we can be doing,” she says. Bourke is working with “leaky dams” at sites in Cork and Wexford, where logs are used as barriers to hold back high-water levels. Unlike beaver dams, they do not reach down to the river bed and so do not flood farmland. She believes that creating a series of these leaky dams, starting in the uplands, can be done at scale and with community support, that would be effective in reducing the impact of downstream flooding and would effectively mimic the work of beavers.

Harty agrees that there’s a lack of trees and woody material in and around our rivers but nevertheless believes there are likely to be some areas that would be suitable for beaver introduction. He thinks step one is to pay farmers a premium for native woodland establishment on either side of rivers. Indeed, both the new Forest Strategy and the Department of Agriculture’s agri-environment scheme, ACRES, provide dedicated measures for this purpose. He thinks that the habitat creation and establishment of beavers would be a five- to 10-year process.

While it may be possible for people to mimic the work of beavers, given the scale of work that is required across Ireland, wouldn’t beavers do a better job and at lower cost?

Would beavers prove to be invasive, in the way that rhododendron or grey squirrels have proven to be? The science suggests this is unlikely, given that, unlike most species which are listed as alien invasive in Ireland, beavers have evolved for millennia in western Europe and alongside the many other species with which they interact. We also seem to be quite relaxed about introducing large numbers of non-native species, such as pheasants or free-roaming sheep, with few or no safeguards for the wider environment. And while it may be possible for people to mimic the work of beavers, given the scale of work that is required across Ireland, wouldn’t beavers do a better job and at lower cost?

At the University of Exeter last April, beaver ecologists and policymakers convened to celebrate the impressive success of beaver reintroductions to date in England and Scotland. In Wales, beavers are being kept under close watch in fenced enclosures at a number of locations, while some breeding in the wild is suspected. There have been some conflicts with local landowners but these are being dealt with. Overall, reintroducing beavers is high return with low impact and low cost. One attendee noted that “beavers are such a different nature story than the one we normally associate with loss and destruction. It is one of renewal and abundance.”

After years of trying to engineer our rivers into submission, there was welcome talk this autumn of changing how we use our land as part of wider efforts to deal with flooding. After Midleton in Co Cork was badly affected, Taoiseach Leo Varadkar said: “We have to consider the impact inappropriate land use can have on flooding and drainage.”

Along with flooding, over half of our rivers are failing to reach “good status”, due largely to pollution from agriculture and human waste, as well as poor “hydromorphology”, a word that describes how the shape of rivers has been altered through arterial drainage and the imposition of dams and other barriers to the movement of fish.

Meanwhile, biodiversity is plummeting, with some of our most endangered species and habitats associated with river systems, such as the freshwater pearl mussel, Atlantic salmon, and native alluvial (swamp) forests.

The task is immense: as well as facing the prospect of runaway climate change, we have legally binding commitments to protect biodiversity and restore all of our water bodies to “good status” by 2027. Why wouldn’t we use the cheapest and most effective tools at our disposal? The science is there to prove how important beavers could be in restoring rivers; it shouldn’t be ignored.

Pádraic Fogarty is an ecologist