 The source of one of these, the Gries, is situated on the Italian southern side of the Gries Pass; another forms beneath the Passo di San Giacomo, others flow from little Alpine lakes such as Lago Castel and Lago di Sabbione.South of La Frua the water of the river plummets over the Cascata del Toce into the Formazza Valley, through which it flows before transversing Valle Antigorio after another series of cascades.Near Crevola d'Ossola the river Diveria flows into the Toce.