Lago di Luzzone, Mountain reservoir in Blenio Valley, Switzerland.

Lago di Luzzone is a reservoir at 1,606 m in the upper Blenio valley, Ticino, held by the curved concrete Luzzone arch dam completed in 1963 and raised 17 m in 1997–1998. The dam's pale grey upstream face, crossed by faint vertical construction joints, closes a narrow valley; a thin parapet and a small box-like structure sit on the crest, and a paved road with a low wall approaches from the left. Behind it the dark blue water fills the basin, its smooth surface cut by narrow inlets, with pale tan banks and a broad shoreline shelf at the dam.

The arch dam Luzzone was completed in 1963, designed by engineer Alfred Stucky. To build it, the capacity of the access road to Blenio was increased and a new road was driven through the Galleria della Töira above the old one. Between 1997 and 1998 the wall was raised by 17 metres, bringing the crest to 1609 m; the reservoir's lowest drawdown level is 1435 m.

The reservoir is operated by Blenio Kraftwerke AG, based in Locarno. Its water is first used at the Olivone power station, then diverted to the Malvaglia reservoir and used again at the Biasca plant. The dam is reached by a winding road from the village of Ghirone.

The dam is reached by a winding road with many hairpins from Ghirone; the road above the old route runs through the Galleria della Töira tunnel, built to raise access capacity during dam construction. A cable car is also kept for winter service. The crest sits at 1609 m, and the reservoir can be drawn down to 1435 m.

The dam wall carries the world's longest artificial climbing route, installed in 1999: over 650 holds and bolts across 165 metres and five pitches, graded 6+/7− on the UIAA scale for the final overhanging section. The lowest holds sit several metres above the ground to deter casual visitors, and use requires a fee and a deposit.