Cornino Lake is a small stretch of water originating during the glacier withdrawal which took place about 10,000 years ago. In that period, several and imposing landslides involved the slopes of the valleys (up to that moment smoothed by the action of the glacier) that were suddenly deprived of the support represented by the ice mass itself.
The current morphology is the result of one of these landslides with an outer bar enclosing a depression upstream. The bottom of this depression is about a dozen of meters lower than the shore of Tagliamento and the waters of the water table of Piana di Osoppo flow into it crossing the permeable sediments of the ancient landslide.
These waters can be easily distinguished from the waters coming from Prealpi for a chemical "trace" characterizing them: coming from the basin of Tagliamento, they are rich in calcium sulphate obtained from the dissolution of the gypsum characterizing its basin, unlike the prealpine basins. The lake also welcomes waters of various origin coming from the plateau of Mt. Prat.