Two beavers introduced to the Forest of Dean to tackle flood risk are being removed due to tapeworm fears.
The creatures were brought back to an area near Lydbrook last year after a 400-year absence, and since then have built five dams.
They were part of a group imported from Bavaria, where one has tested positive for Echinococcus multiocularis (EM).
The beavers will be moved to "biosecure accommodation" and two new ones will take their place, officials have said.
Once tested, the rodents will not return to the Forest of Dean as they are territorial. Instead, they will remain in a secure enclosure for breeding.
A Defra spokesperson said: "As a precaution, the beavers released in 2018 will be further tested and moved to a secure site, where wildlife contact can be reduced and the beavers can be checked regularly.
"A new pair of beavers will be brought to the Forest of Dean from a disease-free source to continue the reintroduction project."
The beaver that tested positive for tapeworm has been put down, officials confirmed.