Potamon fluviatile crabs' unusual size, up to , and longevity (up to 15 years) are also interpreted as evidence of a long-established population, by analogy with island gigantism. On the island of Malta, "Potamon fluviatile" is rare and restricted to a few locations in the west of the island. On Gozo, there is a single population which inhabits a stretch of river only long. In the Balkan Peninsula, "Potamon fluviatile" is known to occur in Croatia, Montenegro, the Republic of Macedonia, Albania and Greece. There are four species of "Potamon" in the Balkans, and "P. fluviatile" is replaced by "Potamon ibericum" in
Potamon fluviatile and across Central Asia as far east as northwestern India. The populations of "P. fluviatile" on the Peloponnese, Kefalonia, and Zakynthos may represent a separate, cryptic species, and the population from the Peloponnese was described in 2010 as "P. pelops". "P. fluviatile" was formerly divided into three subspecies: "P. f. algeriense", "P. f. berghetripsorum" and "P. f. fluviatile". The first two of these live in North Africa, and were later combined and separated from "P. fluviatile" as the species "Potamon algeriense". By 1983, the nominate subspecies (equivalent to the current circumscription of the species "P. fluviatile") had been divided into