Around 30 water voles are being moved from their home near one of Europe's largest sewage plants in east London.
The voles had made their home at Crossness Marshes beside Crossness Sewage Treatment Works.
The people running the treatment works are making it bigger, so want to move the voles away while the work happens.
Wildlife experts have been using apples and carrots to tempt the voles, and once caught they are being moved to the Wildwood Breeding Centre in Kent.
Martin Wagner, Thames Water's conservation manager, said: "With work due to start soon on the planned extension to the works, we wanted to make sure these voles were not disturbed or hurt in any way.
"That's why we're transferring them to a breeding sanctuary in sunny Kent.
"They're likely to stay there for about two years, where we hope their numbers will increase. They will then be brought back to Crossness to enjoy new reed ditches specially created for them."