Schwarzsee, Alpine lake in Canton of Fribourg, Switzerland

Schwarzsee, called Lac Noir in French, is a lake of about 0.5 km² in the Freiburg Prealps at 1047 m above sea level. Its shores are mostly flat and lined with meadows and trees, with a short steep bank only in the south. The German source gives a maximum depth of 6 m, the French one 10 m. It drains north through the Warme Sense.

The sulphur-rich water of Schwarzsee has been used for therapeutic bathing for around 200 years. Since 1937 the lake has hosted the Schwarzsee-Schwinget, a wrestling and alpine festival counted among the important Bergkranz festivals and held annually. In 2021 the LAC-NOIR-Schwarzsee Festival was launched by musician Gustav (Pascal Vonlanthen) and architect Gianni Perotto, and has run every two years in August since.

The lake gives its name to the resort hamlet of Schwarzsee in the municipality of Plaffeien, which has about 500 permanent residents. Since 1937 the Schwarzsee-Schwinget, a wrestling and alpine festival, has been held here annually and counts among the important Bergkranz festivals. Since 2021 an open-air music festival, LAC NOIR Schwarzsee, has taken place every two years in August.

The lake is easily reached on foot via hiking trails that start from several parking areas in the surrounding region. The best time to visit is from May through October, when the weather is stable and the paths are snow-free.

The lake is an official airfield with the ICAO code LSWS; when the ice reaches about 30 cm in winter, aircraft use the frozen surface, and a BAZL drone flight restriction applies over the area. A seven-metre observation tower stands on the Plaffeien shore.