As extreme weather has become more common, interest has been rising in techniques to reduce river flooding. One important strategy is to slow the flow, by creating meanders, flood meadows and ponds. And some have been experimenting with reintroducing beavers, which do this through excavations and dams. Last year we reported on how this is working in Norfolk. But a new study on Norfolk’s river Glaven suggests that beavers might have an additional role in cleaning our rivers, and especially our endangered chalk streams.
The Glaven
The river Glaven is a chalk stream which loops round the North Norfolk market town of Holt, and flows peacefully for ten miles to enter the North Sea near Cley next the Sea. In medieval times, Cley was an active port, but the sea long ago retreated and its now a mile away. The tourists who visit come to walk on the sea wall, photograph the windmill, and shop in the famous delicatessen and fish smokehouse, probably rarely notice the river. But the river has been the site of an important experiment in reintroducing beavers into the rural landscape.
Our rare chalk streams
As we have reported previously, 85% of the worlds’ rare chalk streams are in England, with around 25 in Norfolk. The underground chalk aquifers produce cool, mineral rich water and a clean gravel river bed which is an ideal environment for plant life, invertebrates and fish. As a result, the Glaven is home to sea trout, white clawed crayfish and the endangered European eel, as well as many insects.
But chalk streams are vulnerable to drought, and many have suffered from over extraction of water for crop watering, and from pollution. As a result, less than a quarter of England’s chalk streams are classified as in a ‘good’ ecological state, and none meet EU standards for ‘good’ chemical status. Restoring them is a UK government priority, and in 2021 the Chalk Stream Restoration Group (CSRG), published a strategy to restore Britain’s chalk streams.
Pollution killing wildlife
Pollution is a critical threat to chalk streams. ‘Eutrophication’, is the process whereby an excessive build up of nutrients in the water produces algal blooms and bacterial growth. This reduces the oxygen in the water, making it inhospitable to fish, and potentially poisonous to livestock. Chemically it is the result of excessive levels of nitrates and phosphate. Most commonly this comes from run off of chemical fertilisers and animal waste spread on nearby fields.
Enter the beavers
Two years ago, a team from the University of East Anglia, and the Norfolk Rivers Trust decided to test the impact of beavers on the Glaven. They introduced a pair of beavers into a 6-hectare enclosure of poplar woodland at the head of one of the tributaries of the Glaven and monitored the water quality as it entered and left the enclosure. For comparison they did similar monitoring on a separate tributary of the same river where there were no beavers (the control site). Over two years to May 2024, the original beavers produced four kits, and between them the six beavers created 13 dams, and additional channels. As a result, the water was passing though much more slowly.
Comparisons between the two sites were limited, because the ‘control’ site was less wooded, and more exposed to agricultural runoff. However, it gives an indication of likely water quality in similar chalk streams on agricultural land. And there they found that only 7% of samples met the EU standard for ‘good’ environmental status.
However, in the beaver area, the results were dramatic. Researchers tested the water upstream and downstream of the beaver enclosure, and found that the level of phosphates halved as it passed through (flowing much more slowly as a result of the beaver dams), while for nitrates the drop was 42%. While 44% of samples of the water entering the beaver enclosure met the EU’s ‘good’ standard, when the water left the beaver enclosure, the figure had risen to 75%, a very substantial reduction in pollution.
More to be done
So, there is good reason to believe that more widespread introduction of beavers could not only reduce flooding, but improve water quality and wildlife. As the paper says:
“Overall, these results demonstrate the reestablishment of beaver wetlands could mitigate eutrophication risk, and in so doing support the EU Water Framework Directive goal of achieving ‘good’ physicochemical status in chalk stream catchments.”
Academic research usually concludes that more research is needed, and the researchers point out that this is only one contribution to our knowledge of the impact of beavers, carried out in a carefully controlled area, where the beavers could not escape into the wider environment. Nevertheless, it is an important one.
Polling suggests that most people are in favour of reintroducing beavers in England, but farmers are less enthusiastic. Beavers are Britain’s largest rodents (they can weigh up to 30 kg), they fell trees and flood land, and as a protected species there are tight rules about how to control them. The issue has recently been a big talking point in The Archers.
However, this study does suggest that they may have a serious role to play in restoring one of our unique environments, and the Beaver Trust has published guidance on how farmers and beavers can live together.
Share this article on Bluesky:
More from East Anglia Bylines
