Lake Canterno is a karst lake in the heart of Ernici mountains. The lake originally filled when a karst sinkhole was filled with debris. Then, when the volume water increased so did the pressure, and the hole reopened and the lake emptied, and the cycle recommenced. This natural cycle was interrupted with an artificial closure for the production of electrical energy. The lake is not suitable for swimming and is part of the Nature Reserve of Lake Canterno.