Just 30 years ago the banks of the River Colne, in Essex, would have been teeming with water voles. But the population was wiped out by mink.
Now, with the mink gone, The Woodland Trust is delighted to be able to re-home 300 water voles, bringing the species back to the area.
Thousands of animals are being moved from the London Thames Gateway to allow for construction.
And the water voles have been moved to Fordham Hall Estate - a Woodland Trust wood on the banks of the Colne.
You can see the little creatures being rehomed on The BBC's Countryfile.
(The feature begins 38 minutes into the programme.)