Bortelsee, Reservoir in Ried-Brig, Valais, Switzerland

Bortelsee, also marked Bortelseewji on the national map, is a reservoir at 2,463 m above sea level near the Bortelhorn above Brig, Valais. Its water is held by a rockfill dam built in 1988 and 1989 in a construction period of eighteen months; the lake holds 1.7 million cubic metres.

The Bortelsee dam, a rockfill embankment, was built in 1988 and 1989 in about eighteen months to impound 1.7 million m³ of water at 2,463 m above sea level. After floods in 1993 and 1994, the spillway was modified in 2000, and in 2005 the air-side embankment was enlarged to meet federal water and geology office guidelines.

The lake is accessible via marked trails and serves as a stopping point during mountain walks in the area. Visitors should prepare for exposed mountain conditions, which can be cool and windy at this elevation.

Bortelsee sits at 2,463 m, making it one of Switzerland's highest reservoirs built for power generation. Its water can produce 3.5 kWh per cubic metre, among the highest energy equivalents in the country, and is used mainly in winter for peak power.