Postafibreno lake

Italy, thanks to its geological conformation and its origin is particularly rich in calcareous outcrops, that is some rocks which are originated by marine sediments layed down in a typical marine pelagic environment. From the Sicily to the Apulia, to the Alps and Apennines chains there is a lot of evidences of this phenomenon: superficial forms such as doline, polje, karren or underground forms such as grottos, galleries o wells.
To understand the entity of this geological phenomenon, it is suffice to say that about 44% of the Italian mountain areas are interested by karst events with a correlated underground water circulation which flow into spring water or directly in the sea. A similar phenomenon is Postafibreno Lake, in central Italy.
The lake is located in proximity of Posta, a locality which was used anciently like an area for exchanging horses which were used for the delivery of the mail between Rome and Naples. Located on the slopes of the Apennine chain, on the south side-west of the Mountains of the Marsica (central Italy), the lake has to its origin to a system of pedemontane sources which derived from the hydrological basin of the high Valley of the Sangro, in the National Park of Abruzzo.
Considered as a source, even though of considerable flow (about 9 m3 /sec), has a tight and extended shape; after its expansion it gives the origin to the river Fibreno -also called in the past "river of Cicero" because it licked the funds of property of the large Roman speaker- before flowing into in the river Liri.
Thanks to its karstic origins, this lake has a temperature of around 10°C (50°F) throughout the year. It has a surface of about 0.287 km2 and a maximum depth of 15 m, which are reached only in a small area. For its extended shape, the high capacity of water exchange, the temperature nearly costant during all the year, it was often considered a lake-river more than a simple lake.