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.
Divisive debate with party-political friction as Devon’s budget approved
Council tax will rise
Call for West Devon to be split to get best for residents
Residents in the north look to Exeter; and to Plymouth in the south
Dartmouth residents bemoan year-long closure of key road
Residents submit petition with around 2,500 signatures calling for action
Hard up charity will get more help from lottery cash
Citizens Advice helped more than 3,000 in North Devon over six months
Campaign for emergency phones at bridges to save lives
Temporary mobiles are in place at the moment
Man missing from Exeter area
Have you seen Matthew Welham?
