A large northern tributary of the Puelo, the Manso, has its sources in Mascardi Lake and other lakes and streams south-east of the Cerro Tronador, also in Argentina, and flows south-west through the Andes to unite with the Puelo a few kilometers west of the 72nd meridian. Puelo river's lower course is impeded in such a manner as to form three small lakes, called Superior, Inferior and the Tagua Tagua Lake.