Included between the municipalities of Fiuggi, Fumone, Ferentino and Alatri, Lake Canterno is a karst basin It is the largest of the karst lakes in Lazio: it has an area of 0.6 square kilometers, a perimeter of 4.9 km and a maximum depth of 25 meters.
The lake in Ciociaria bathes four municipalities: Ferentino, Fumone, Fiuggi and Trivigliano. Even though it is located near busy provincial roads, Lake Canterno has managed to keep its atmosphere intact. It is surrounded by woods of oaks, Turkey oaks and broadleaf trees and allows visitors to admire the grey heron, the red heron and the moorhen.The greatest mystery that surrounds Lake Canterno and the same that gives it the nickname of ghost lake, is a singular phenomenon of instability, due to the moments when the river Pertuso emptied and filled. The lake, at regular intervals, would dry up either partially or completely, and then suddenly appear in all its width. There were phases of drying up that could last days, months or even years: the longest lasted from 1894 to 1943. The phenomenon of the periodicity of the lake continued in an eloquent and spectacular way for 12 times until 1923, but it was definitely reduced in 1945, after about 20 years of dryness, with the artificial obstruction of the swallow hole and the realization of a small hydroelectric power station. In 1943, meanwhile, it was possible to carry out the first exploration of the "Pertuso", and it was discovered that it communicated with an underground cave, one of the many karst cavities in the area. It was only then that it was understood where the fish took refuge during periods of water shortage, a fact that had remained unexplained until then. Although today efforts are made to regulate the volume of the basin, its natural peculiarity of being unstable has not disappeared completely. On the contrary, it manifests itself more constantly, although in a less spectacular way than in the past.
