Potamon fluviatile and covers parts of many countries with a Mediterranean coastline. It is found in mainland Italy and on the Balkan Peninsula from Dalmatia to the Axios River in Greece. It is also found on a number of islands, including Sicily, Malta and Gozo, the Ionian Islands, Aegean Islands, Sporades and Andros in the Cyclades. Although the species as a whole is widespread, it is declining in numbers, and these insular populations are particularly vulnerable. "Potamon fluviatile" is widely distributed in much of mainland Italy, especially in the provinces of Trento, Lombardy, Veneto, Liguria, Tuscany, Umbria, Lazio, Campania, Apulia, and Calabria,
Potamon fluviatile six "nationes", or "tribes". Natio "fluviatilis" was found in northern Italy, natio "tarantium" in southern Italy, and nationes "thessalonis", "kühnelti" and "laconis" were found in parts of Greece. The geographical distribution of natio "leucosis" was not reported, and it was suggested that a further (undescribed) tribe inhabited the Greek island of Andros. Despite this wealth of infraspecific taxa, they are rarely used by scientists, and some have questioned directly the value of defining infraspecific taxa within "P. fluviatile". In 1990, the population on Malta was described as a separate subspecies, "Potamon fluviatile lanfrancoi", and that taxon has become a conservation