The Cervo stream rises from Lago della Vecchia, at 1,868 m altitude, and gives its name to the long and narrow valley that culminates with the typical village of Piedicavallo. This valley, fresh in summer, but extremely cold and snowy in winter, preserves ancient traditions, legends and esotericism, which envelop in mystery in particular the picturesque village of Rosazza. Going down to the valley, after collecting the waters of the Oropa stream, the bed of the river widens and laps the plateau of the Baraggia, before finally flowing into river Sesia, after a course of almost 65 km.