Wild swimmers are safer in lakes, rivers, and ponds inhabited by beavers, according to a new study.
Researchers at the University of Stirling in Scotland have uncovered that beaver dams drastically improve the water quality of British eco-systems.
Their work, detailed in the Science of the Total Environment journal, monitored how rodent populations affect pollution levels in British waters. For more than two years, researchers sampled water from different beaver-engineered water systems and found that dams reduce ‘pollution peaks’ by up to 95%.
Beavers build dams using logs, branches, rocks, and mud, which slow the flow of water and create ponds. This process traps harmful microbial pollutants like E.coli, which silts and settles near the dams, cleaning the water for wild swimmers downstream.
"These ponds act as natural traps for pollutants and silt, especially when muddy or contaminated water flows in from upstream," co-author Nigel Willby told The Times.
“The result is not only a reduction in pollution but also a delayed movement of contaminants, which benefits downstream ecosystems."
Described as a ‘chemical cocktail’ by lawmakers, British and Northern Irish waters have been bombarded with pollution in recent years. Thanks to the excessive use of pesticides and fertilizer, and the release of untreated sewage, many previously popular swimming spots are now avoided.
Pollution has had a devastating effect on the UK's wild swimming community. Last summer, at least 35 athletes fell ill after swimming in the River Thames during the Royal Windsor Triathlon. There were several other similar incidents throughout 2024.
Microbial pollutants like E.coli are particularly dangerous to wild swimmers and can cause various gastrointestinal illnesses and infections.
Check out our expert guide for information on how to stay safe and avoid illness while wild swimming.
Beavers became extinct in Britain more than 400 years ago due to excessive hunting.
In 2002, rogue rewilders released beaver families in Kent to improve the local habitat. Illegal releases were followed by an official re-introduction program seven years later. There are now more than 400 beavers in Britain.
Beaver-built dams typically range in size from a few feet to upwards of 300 feet / 91m. The world's largest known dam spans 2,543 feet / 775m in Wood Buffalo National Park in Alberta, Canada.
Last month, beavers in the Czech Republic gained notoriety by building a network of dams exactly where authorities had been planning to construct them.
Officials at the Brdy protected landscape area had just gained approval for the project, which would've set them back the equivalent of $1,257,000 (USD) when beavers spontaneously built the structures.
Experts assessing the work said beavers usually do a better job at dam building than humans.
"Beavers always know best," Jaroslav Obermajer, head of the Central Bohemian office of the Czech Nature and Landscape Protection Agency told Radio Prague International.
He added: "The places where they build dams are always chosen just right - better than when we design it on paper."
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