The primary inflow into Mascardi Lake is the Manso River which emerges from a small lake fed by a glacier called the Ventisquero Negro (literally black snowfield), on the slopes of Tronador mountain about west of the lake. The Manso emerges from the southwestern corner lake via a short, turbulent passage called Los Rapidos (The Rapids) which leads to the Las Moscas Lake, the next in a chain of lakes along the Manso River.