Vättern is the second largest lake (by surface area) in Sweden, after Lake Vänern. It is a long, finger-shaped body of fresh water in south central Sweden to the southeast of Vänern pointing at the tip of Scandinavia.
One of the etymologies for name Vättern is from "vatten", the Swedish word for water. This origin is, however, unclear and in dispute. It has also been suggested that the archaic term "vätter", meaning forest or lake spirits, is the origin of the lake's name.
The lake's total surface area is about 1,912 km², with a drainage basin a little over double that, about 4,503 km². The deepest known point, located to the south of the island of Visingsö, is 128 meters. The average depth is 40 meters. The lake has a perimeter of about 642 km. The volume is 74 km³. These numbers tend to be fixed, as the level of the lake is regulated.
Situated in Götaland, the lake is drained by Motala ström, starting at Motala, and flowing ultimately through a controlled canal into the Baltic Sea. The lake includes the scenic island of Visingsö, located outside Gränna. Other towns on the lake include Vadstena, Jönköping, Hjo, Askersund, Åmmeberg and Karlsborg. It is bounded by the Provinces of Västergötland, Närke, Östergötland and Småland.
In the north there is a scenic but not mountainous inland fjord, Alsen. About 62% of the drainage basis is still covered with spruce, pine and deciduous forest. About 26.7% is dedicated to agriculture.
The geology of the lake is closely bound to that of the Baltic Sea, of which it was often part. The lake, with Vänern, was part of a connecting waterway system through central Sweden to the Skagerrak several times in the recent geological past.
The lake began as an independent body of water left by the receding Scandinavian glacier. It soon became part of the Baltic ice lake. Subsequently it was a bay of Yoldia Sea and then became connected to Ancylus Lake. At about 8000 BP an accident of the uneven Scandinavian isostatic land rise brought Vättern above Ancylus and the two became distinct.
The lake contains both phytoplankton and zooplankton, such as Copepoda and Cladocera. The benthos species include Crustacea, Oligochaeta, Diptera and Bivalvia. In addition are several species of fish, including Salvelinus salvelinus, Coregonus lavaretus and Salmo salar. The lake is known for its Vättern char, as it is called, Salvelinus alpinus.
It is said that there's a lake monster inhabiting Vättern. This is however not nearly as famous as the one supposedly living in Storsjön.
Vättern has been famous for the excellent quality of its transparent water. Many of the municipalities in the area receive their drinking water directly from Vättern. The lake water requires very little treatment before being pumped into the municipal systems and the natural, untreated water can be safely drunk from almost any point in the lake. It has been suggested that Vättern is the largest body of potable water in the world. The surrounding municipalities process their sewage 100%.
Vättern is known for the annual recreational cycling race Vätternrundan, attracting some 15,000 participants to finish the 300 km trip around the shores of the lake.
Vättern is also noted for its fishing, serving people in the nearby districts. Tourist sport fishermen and vacationers are free to fish in the lake as long as they don't use nets. The lake is also used for commercial fishing.
A number of industries provide employment in the drainage basin: mining, manufacturing, forestry and paper. Agriculturalists raise cattle, sheep, swine and poultry.
