Beavers should be reintroduced into the wild to help clean up polluted rivers and stem the loss of valuable soils from farms, new research suggests.

The study, by scientists at the University of Exeter, found that a single family of beavers removed high levels of sediment, nitrogen and phosphorus from water that flowed through a 2.5 hectare enclosure in Devon.

The group of beavers, which have lived in fenced-off site at a secret location in West Devon since 2011, have built 13 dams, slowing the flow of water and creating a series of deep ponds along the course of what was once a small stream.

Researchers measured the amount of sediment, phosphorus and nitrogen in water running into the site and then compared this to water as it ran out of the site after it had passed through the beavers’ ponds and dams system.

They also measured how much of the chemicals, and sediment had been rapped by the dams in each of the ponds.

The results showed the dams had trapped more than 100 tonnes of sediment, 70 per cent of which was soil, which had eroded from ‘intensively managed grassland’ fields upstream.

And that sediment contained high concentrations of nitrogen and phosphorus, which are nutrients known to create problems for the wildlife in rivers and streams and which also need to be removed from human water supplies to meet drinking-quality standards.