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.
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 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.
It is said that there's a lake monster inhabiting Vattern.
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.