It is born from the homonym glacial lake, situated to the east of the Nevado de Longaví, a stratovolcano in the Andes of central Chile. Through its upper section it flows west of the Melado range, surrounded by high Andean mountains. In this first stage it receives several streams specially on its northern side. From the lake the water falls, creating an impressive cascade, to the area known as Bajo de las Lástimas; (a translation would be Lowlands of Sorrow - the explanation is that in the area lies a trail for cattle which, at this section, is extremely difficult for the animals to negotiate).