Last week, 140 water voles were transported from outdoor breeding pens at the Derek Gow Consultancy in Devon to the waterways of Kielder for release.
It takes the total released since the first release in June 2017 to 1,638.
The water voles were the fourth generation of voles that were originally captured for the project from the North Pennines, North Yorkshire and The Trossachs.
They were released from 43 pens containing either sibling groups or pairs across three sites: tributaries of the Tarset Burn on the eastern edge of Kielder Forest.
The original releases back in 2017 were north of Kielder Village.
The project team has slowly worked around the north of the Kielder Reservoir and has now reached the Tarset Burn.
The new release sites are only a few kilometres away from last year’s sites so they should be able to mix as they find their own territories.
Led by Kelly Hollings and Graham Holyoak, staff and volunteers have put the Kielder voles in smaller streams and ditches, their preferred territory judging by recent releases.
Graham, Restoring Ratty project officer said: “Our water vole releases over previous years have provided great joy for people of all ages, including local school children who had the experience of a lifetime helping the project team.
"Unfortunately, this year due to Covid-19, social distancing rules and schools being closed, things were different and it was down to the Northumberland Wildlife Trust’s small conservation team to fill the gap.
“The voles would have to have been released one way or another and the welfare of the animals, as well as the safety of the staff was the priority.”
The next release is in August with more voles coming up from Devon.
Now in its fourth year, and with one year left to run, the Restoring Ratty project has all been made possible by National Lottery players through a grant from The National Lottery Heritage Fund.