or is a lake in Røyrvik Municipality and Lierne Municipality in Trøndelag county, Norway. The 100.18 km2 lake lies just south of the large lake Limingen, and just west of the border with Sweden. It is 358 m above sea level and has a volume of 8.816 km3. The deepest part of the lake is 222 m deep. It is the seventh largest lake in Norway.

Islands

The 6.1 km2 island or lies in the lake Tunnsjøen. The island's highest point is 812 m above sea level; which is 454 m higher than the lake. The peak is named Gudfjellet (lit. 'God's Mountain'). This makes Gudfjelløya the highest island within a lake in Norway (and in Europe). It towers higher than the island of Monte Isola within Lake Iseo, in northern Italy. The island is located in the lake's central part. To the southwest of the island is the lake's second largest island:, also known as Litlfjelløya or (lit. 'Little Mountain Island' or 'Reindeer Island'). Its highest point is 177 m above the lake's water surface.