Tinnsjå ( eng, Lake Tinn), also called ''Tinnsjø'' and ''Tinnsjøen'', is one of the largest lakes in

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and the ...

, and one of the deepest in Europe. It is located between the municipalities of

Tinn Tinn is a municipality in Telemark in the county of Vestfold og Telemark in Norway. It is part of the traditional regions of Upper Telemark and Øst-Telemark. The administrative centre of the municipality is the town of Rjukan. The parish of ...

and

Notodden Notodden () is a city and municipality in Vestfold og Telemark county, Norway. It is part of the traditional region of Øst-Telemark. The administrative centre of the municipality is the city of Notodden. Notodden was separated from the munic ...

Vestfold og Telemark Vestfold og Telemark (; ) is a county under disestablishment in Norway. The county is the southernmost one of Eastern Norway and consists of two distinct and separate traditional regions: the former counties of Telemark and (most of) Vestfold ...

county. At its source in the west, the

Måna The Måna or Måne is a river in Tinn in Vestfold og Telemark, Norway; it flows from Møsvatn through Vestfjorddalen and Rjukan to Vestfjorden in Lake Tinn. It is part of the Skiensvassdraget drainage basin A drainage basin is an area of l ...

river flows out of

Møsvatn Møsvatn (or Møsvann) is the tenth-largest lake in Norway with a surface area of 78.31 km2. It lies primarily Møsstrond, Vinje in Vestfold og Telemark. The lake lies in the watershed of the Skien river (''Skiensvassdrag'') and discharges ...

and past

Rjukan Rjukan () is a town and the administrative centre of Tinn municipality in Telemark, Norway. It is situated in Vestfjorddalen, between Møsvatn and Lake Tinn, and got its name after Rjukan Falls west of the town. The Tinn municipality council gra ...

into Tinnsjå. From the north, the river Mår flows from the Mår, Gøystavatn, and

Kalhovdfjorden Kalhovdfjorden is a lake belonging to the municipality of Tinn in Vestfold og Telemark county in southern Norway. Kalhovdfjorden belongs to the catchment of the river Skien. The river Mår comes out of the lake. The lake is part of the Skiensva ...

lakes into Tinnsjå. Tinnsjå is part of the Skiensvassdrag, and drains via the

Tinnelva Tinnelva is a river in Notodden, Vestfold og Telemark, Norway. It flows from Lake Tinn to Heddalsvatnet. The waterfalls Årlifossene, Grønvollfoss, Svelgfoss and Tinnfoss are exploited, and the hydroelectric power stations have a combined installe ...

river in the south, down to

Heddalsvatn Heddalsvatnet ( en, Lake Heddal) is a lake in the municipalities Notodden and Sauherad in Vestfold og Telemark, Norway. The main influx comes from the rivers Tinnelva and Heddøla. The lake covers an area of 11.9 km2 or 13.2 km2 according to NVE. T ...

. In 1944, during the German occupation of Norway, the ferry SF ''Hydro'' was sunk in Tinnsjå by the Norwegian resistance. The Germans were using the ferry to transport a large quantity of heavy water to Germany, where it was to be used for nuclear weapon research. The heavy water had been produced at

Vemork Vemork is a hydroelectric power plant outside Rjukan in Tinn, Norway. The plant was built by Norsk Hydro and opened in 1911, its main purpose being to fix nitrogen for the production of fertilizer. At opening, it was the world's largest power pl ...

, a factory located in

. The wreck of the ferry was discovered in 1993. In 2004, it was investigated and filmed for an episode of NOVA; heavy water samples were recovered and

deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one ...

isotopic enrichment Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. The use of the nuclides produced is varied. The largest variety is used in research (e.g. in chemistry where atoms of "marker" ...

was confirmed. In 2004 a film crew shooting footage for a new documentary on the heavy water sabotage became aware of an unusual fish, swimming near the lake bottom at a depth of 430 m. Two specimens of the previously unknown fish were captured in April 2005. Analysis revealed the fish to be closely related to

Arctic char The Arctic char or Arctic charr (''Salvelinus alpinus'') is a cold-water fish in the family Salmonidae, native to alpine lakes and arctic and subarctic coastal waters. Its distribution is Circumpolar North. It spawns in freshwater and populat ...

. The light-colored, translucent fish is up to 15 cm long and lacks a swim bladder. Mosvatn

References

Lakes of Vestfold og Telemark Notodden Tinn {{VestfoldTelemark-geo-stub