All surrounding rivers are diverted into the reservoir, among them the Rein da Tuma, coming from Lai da Tuma (Tomasee), near the Oberalp Pass and known as the source of the river Rhine. The Vorderrhein, or Anterior Rhine as the Rhine is called in this area, passes just about 2 kilometers north to the barrier of the lake. A multiday trekking route is signposted along the young Rhine called Senda Sursilvana, from where the barrier can be spotted easily.