Water voles are due to be re-released into the wild after being taken to safety during construction work.
A new business park being built at junction 25 of the M5 posed a threat to the voles' habitat in Henlade Stream in Taunton, Somerset.
As a result 40 of the animals, including some babies, were taken into captivity for safety in October 2019.
Builders say the works have given "careful consideration" to the stream and the voles' habitat.
The water vole is fully protected under the Wildlife and Countryside Act 1981, making it illegal to damage or obstruct access to water vole burrows.
Now building work near the stream has been completed, the voles will be gradually released back on to the site over the weekend of 5 and 6 September.
Vole specialist Jenny Tratt, from Derek Gow Consultancy, said a section of the stream had been fenced off and "re-vegetated" to make sure the voles' habitat was "not touched by the construction at all".
She said: "Out here they're going to be quite happy moving on to something a bit greener.
"Hopefully they'll be off when we come back on Monday, there'll be none of them there, we'll pick the pens up and we're good to go."
It is thought about 94% of the UK's vole population has disappeared, the victims of changes in farming practices, the loss of wetlands and the American mink, which is a ferocious predator.