| Lys | |
| Map: | Lys (rivière).png |
| Source1 Location: | Monte Rosa |
| Source1 Coordinates: | 45.8833°N 7.8111°W |
| Mouth: | Dora Baltea |
| Mouth Coordinates: | 45.59°N 7.7925°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Italy |
| Length: | 40km (30miles) |
| Source1 Elevation: | 2500m (8,200feet) |
The Lys (Walser German: Liisu or Lyesu) is a small 40km (30miles) river (classified as a torrente).
It flows from the Lys Glacier on the south side of the Monte Rosa massif, at the foot of Vincent Pyramid, elevation 4215m (13,829feet), and runs through the Gressoney Valley, flanked by a road, through the following municipalities:
It converges with the Dora Baltea (fr. Doire baltée) as a right tributary at Pont-Saint-Martin.
Its left-side tributaries are Avant-Cir, Glassit, Loo, Mos, Niel, Pacoulla, and Tourrison. From the right it receives: Rû de Nantay, Stolen and Valbona.