The Brenta river starts between the "Caldonazzo" and "Levico" lakes, two small lakes in the Trentino-Alto Adige/Südtirol region, in the comune of Caldonazzo, Trento province, at an elevation of about . From here, the river flows through the "Valsugana", the valley that goes from Bassano del Grappa to Trento, first to the east and later to the south. In this part, the Brenta is joined by its main left tributary, the Cismon stream, in the "comune" Cismon del Grappa, province of Vicenza (the Bacchiglione river is larger but it joins the Brenta near the mouth).