Gigerwaldsee, reservoir in Pfäfers, Canton of St. Gallen, Switzerland

Gigerwaldsee is a reservoir in the Calfeisental valley, in the municipality of Pfäfers, Canton of St. Gallen. Its arch dam, the Gigerwald, was completed in 1976 and stands 147 metres high. The reservoir holds 35.6 million cubic metres of water and covers 71 hectares, making it the largest lake entirely within St. Gallen.

The dam was completed in 1976 and stands nearly 150 meters high to store water for electricity generation. Before its construction, the valley was wild mountain terrain with a small stream where the Walser community of Sankt Martin had settled.

The name references the valley and waters that draw visitors since the 1970s. The area is shaped by the Walser people, an alpine community whose traditional homes still stand in nearby Sankt Martin.

The southern shoreline is easy to reach on foot, with marked trails and a popular route to the Walser village of Sankt Martin. Visitors should look for the four lit tunnels along the road, which offer views of the water and mountains.

The reservoir is the largest lake lying entirely within Canton St. Gallen. Its water comes from the upper Weisstannental, Calfeisental and Taminatal valleys and feeds the Sarganserland pumped-storage plant, which produces an average of 460 million kWh a year. Sediment raises the reservoir floor by about 40 cm annually, so the bottom outlet was raised by 20 metres during the 2024 renovation.