Beavers can help clean polluted rivers and reduce soil loss from farmland, according to a study by Exeter University and the Devon Wildlife Trust.
They looked at a captive colony of beavers in Devon, analysing water before and after it passed through their dams.
They discovered that the dams act as a filter, trapping soil which has run off from farmers' fields, and which contains nitrates and phosphorus from fertilisers..
These chemicals are not allowed into the drinking water supply.
Top up payments for Ukrainian hosts in North Devon
Households in the area to receive £425
North Molton storm overflows halved
Water storage tank added at treatment works
Devon County Council elections - all the candidates, all the wards, all the key dates
All the information you need
Exmoor Coaster service coming back under different name
'Explorer' subsidised by county councils
Bodmin Moor fires are suspicious
Police asking for help over blazes on Saturday
Storm overflow prevention work set for Plymouth
But it will take five years
