The pool frog (Rana lessonae) went extinct in the wild in the UK between 1993-95. The last known site was in Thetford, Norfolk. Apparently it was only recognised as a species internationally a few decades before its extinction.
However nowadays we recognise biodiversity and there is a strong populations of pool frogs in Sweden of the same race. Natural England and the Herpetological Conservation Trust are quitely running a programme which has involved annual spring imports, the last occurred this year.
The site in Norfolk is being kept secret but according HCT trustee Howard Inns
The frogs already established at the release site, a complex of some 13 separate ponds, bred successfully in small numbers, and newly emerged froglets were found at the end of the season.
All aspects of the project continue to be closely monitored and individual pool frogs are photographed and identified by differences in their dorsal and lateral markings.
He added that studies showed the frogs are in good condition and capable of growing rapidly at the reintroduction site. After the programme's completion, "close monitoring will continue as a means of helping to determine the next steps in this initiative to re-establish this interesting and attractive species as a thriving resident.