Kallsjön, Deep glacial lake in Jämtland, Sweden

Kallsjön is a deep glacial lake in Jämtland with a maximum depth of about 134 meters and significant freshwater volume. The water is surrounded by dense forests, with several natural shoreline areas accessible to visitors.

Kallsjön has been regulated for hydroelectric power since the early 1940s. Its outlet is at the southern end, where the Järpströmmen stream flows down to Järpen and into the Indalsälven. The lake covers 158 square kilometres, reaches a depth of 134 metres and lies 382 metres above sea level.

The lake serves as a gathering place for water sports enthusiasts throughout the year, drawing people who come to fish, swim, and surf. The wooded shoreline provides several access points for visitors to reach the water.

The southern shoreline is most accessible with several entry points for different activities. The best conditions for water sports occur during north to north-northwest winds, especially in winter months.

The name Kallsjön has nothing to do with cold: it comes from the old dialect word for "fellow", and the original name Kalln referred to a man named Karl said to be related to the god Frö, who gave Frösön in Storsjön its name.