Lago Piatto (Italian lago lake, piatto plate, "plate lake") is a lake in the Province of Pistoia, Tuscany, Italy.
Besides Mosso and Valle Mosso other municipalities of the area are Cossato (a town which lies in the main valley near its exit on the Po plain) and Bioglio, Callabiana, Camandona, Crosa, Lessona, Piatto, Pettinengo, Quaregna, Ronco Biellese, Selve Marcone, Soprana, Strona, Ternengo, Trivero, Vallanzengo, Valle San Nicolao, Veglio, Zumaglia.
Valle San Nicolao borders the following municipalities: Bioglio, Camandona, Cossato, Pettinengo, Piatto, Piedicavallo, Quaregna, Scopello, Strona, Trivero, Vallanzengo, Valle Mosso.