Rein da Medel is the local Sursilvan, (i.e. Romansh) name in Graubünden, which is commonly used to denote the ticinese part as well.

The headwaters of the Rein da Medel flow through the Val Cadlimo, a small west-east valley south of the main Alpine ridge in the municipality of Quinto in the canton of Ticino.

The southern and western spring creeks are about 1,000 meters from their start to the confluence before the Lago dell'Isra (2,321 m (7,615 ft)).

A few meters north of the inflow into the Lai da Sontga Maria reservoir (1,906 m (6,253 ft)), the boundary between Ticino and Graubünden is a straight line between Lukmanier Pass and Pizzo Scai, which ignores the local topography.

The name change takes place at the confluence of major tributary Rein da Cristallina down from south-east.