Lases Lake is the twin of that of the Valley with which it is linked by a permanent issue of water flowing underground.
It is on the watershed between Avisio and Fersina. The lake is probably of tectonic origin. It has an elongated shape: wider at the northern end, with an attractive reed bed between the two beaches nearer the town, and narrower to the south where the reeds and marches are enclosed within a gorge.
This is the most interesting stretch, because it is the habitat of many rare species of flora and fauna, now protected by the constitution of a provincial biotope.