Pool frog – Pelophylax lessonae

The uniform distribution area of the pool frog covers most of Europe. In the north, it extends to the Baltic Countries, but not to Denmark. In most of its range, the pool frog lives in mixed populations with the edible frog.

In the Nordic countries, the pool frog can only be found in two separate relict deposits, one located on the coastal area southeast of Gävle in the province Uppland in Central Sweden, and the other one in the County East-Agder in Southern Norway. In Sweden, the species is classified as endangered and it only occurs in about 90 ponds in the vicinity of the sea in Uppland. In Norway, the population size varies from 15 to 50 adults depending on the annual reproductive success, and the species is critically endangered in the country. The populations in Sweden and Norway are relics from the thermal period that followed the last ice age, and they are exceptional also because the occurrences seem to be clean of edible frogs.

In Finland, reportedly the nearest pool frog populations are located in the archipelago of Uppland in Sweden and, possibly, in the Northwest corner of Estonia. The origin and the history of dispersal of the Finnish pool frogs are unknown. The species may have arrived in Finland intentionally or unintentionally by human. Considering that in the Uppland archipelago, the pool frog has been able to colonise islands and islets located quite far from the coast, it may be possible that the species has naturally spred to Finland.

Also the pool frog populations in Finland appear to be clean, because no edible frogs have been found in their ponds.