Beavers were reintroduced on the river Otter by the Devon Wildlife Trust six years ago, in what was deemed “a success story”.
But conservationists are concerned that sewage being discharged weekly from a storm overflow site upstream could impact the colony of about 20 families.
According to the Times, South West Water’s overflow site at Honiton, which flows directly into the river Otter, spilt 137 times last year, totalling 2,442 hours of spillage.
Mark Elliott, who oversees the beaver project at the Devon Wildlife Trust told the Times that the discharges were of concern.
He added: “There is a whole range of nasties contained in sewage that could potentially impact them, like viruses and bacteria.”
In a statement, the Devon Wildlife Trust said it would continue to monitor the local beaver population to see if there is a detectable impact from recent incidents.
“Pollution into any river or stream is a serious issue. Most of the UK’s rivers are in a deplorable state. Clean watercourses are vital for the people and communities who live alongside them, as well as for the wildlife that they support,” it said.
A spokesperson added that “beavers are large, mobile and robust animals, and while they spend large amounts of time in the river, their food sources are on land – namely bankside trees, grasses and other plants. This means they are not necessarily the best indicators of the full seriousness of pollution incidents”.
But the trust added that through dam building, beavers create the space and conditions for other species making rivers and wetlands healthier and richer in other wildlife.
“The biggest impact of pollution in rivers will be to reduce this positive impact, reducing the benefits which beavers can have in restoring our rivers and the nature they support,” the spokesperson added.
The trust also noted that pollutants from other sources such as run-off from farmland, were of concern.
South West Water said it had been working with farmers in the river Otter catchment since 2015 and this has done much to reduce the input of pesticides and other farm run-off into the river to protect its overall river quality.
A spokesperson added: “There are many wild living beavers across the rivers throughout the South West. As they are expanding to new territories we are totally committed to the sustainable management of wild living beavers and supporting their habitats, due to the multiple potential beneficial impacts beavers can have on rivers.”