Lac de Bret, Reservoir in Puidoux, canton Vaud, Switzerland

Lac de Bret is a lake in the municipality of Puidoux, canton Vaud, Switzerland, north of Lake Geneva at 674 m elevation. It lies in a depression formed by a moraine blocking a glacial valley. The lake is about 1.5 km long and 400 m wide, with 4.1 km of shoreline, a surface of 0.36 km², a volume of 5 million m³ and a maximum depth of 20 m.

The first dam at the lake was constructed in 1875 to supply water for the Lausanne-Ouchy funicular, a cable car system carrying passengers up and down the hillside. The lake later became a drinking water reservoir for the nearby city of Lausanne and remains an important water supply for the region today.

The name Bret derives from Old German brestan (to break); records name it Bryt in 1529, Brel in 1590, Bruict in 1650 and Lac de Bro on Antoine Chopy's 1730 map. Since 1871 its water has driven the Lausanne-Ouchy funicular, and since 1957 the Lausanne water service manages it.

The lake lies at 674 m in Puidoux, between the Gourze tower to the west and the Chesau and Pélerin mounts to the east. Its shores run 4.1 km, and the water intake sits 11 m deep, so the level can drop by several metres depending on the treatment plant's draw; a minimum level is guaranteed. In winter the surface often freezes over completely.

The lake's water comes from the Grenet stream 350 m to the north, which belongs to the Rhine basin; a diversion built in 1875 carries it over the watershed into this Rhône-basin lake, raising its catchment from about 2 km² to roughly 21 km². Before that, only runoff and underwater seepage fed it.