| Caption Map: | Interactive map of the lake |
| Coordinates: | 64.705°N 13.2116°W |
| Location: | Lierne Municipality and Røyrvik Municipality, Trøndelag |
| Type: | glacier lake |
| Inflow: | Ingelsvasselva, Mykkelvikelva, Rørvasselva and Stallvikelva |
| Outflow: | Tunnsjøelva |
| Catchment: | 388.68km2 |
| Basin Countries: | Norway |
| Length: | 20km (10miles) |
| Width: | 10km (10miles) |
| Area: | 100.18km2 |
| Depth: | 88m (289feet) |
| Max-Depth: | 222m (728feet) |
| Volume: | 8.816km3 |
| Shore: | 118km (73miles) |
| Elevation: | 358m (1,175feet) |
| Islands: | Gudfjelløya and Litlfjelløya (or Reinøya) |
| Reference: | NVE[1] |
or [2] is a lake in Røyrvik Municipality and Lierne Municipality in Trøndelag county, Norway. The 100.18km2 lake lies just south of the large lake Limingen, and just west of the border with Sweden. It is 358m (1,175feet) above sea level and has a volume of 8.816km3. The deepest part of the lake is 222m (728feet) deep. It is the seventh largest lake in Norway.[3]
The 6.1km2 island or lies in the lake Tunnsjøen. The island's highest point is 812m (2,664feet) above sea level; which is 454m (1,490feet) higher than the lake. The peak is named Norwegian: Gudfjellet . 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 Norwegian: Litlfjelløya or . Its highest point is 177m (581feet) above the lake's water surface.