Vättern

Vättern (/ˈvɛtərn/ VET-ərn, Swedish: [ˈvɛ̌tːɛɳ]) is the second-largest lake in Sweden, after Vänern, and the sixth-largest lake in Europe. 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. Vättern is deep, containing roughly half as much water as Vänern even though it covers about a third as much area; its deepest point is 128 metres (420 ft) below sea level.

Vättern drains into Motala ström through Bråviken into the Baltic Sea, but since 1832 it has also had a downstream connection through the Göta Canal to Vänern and the Kattegat tributary of the Atlantic Ocean. The lake has plenty of sources from rivers and small lakes, with the highest located sources being near Nässjö on the South Swedish Highland near the southeastern shoreline.

The name Vättern is closely related to "vatten", the Swedish word for water, and also means "water, lake".

The lake's total surface area is about 1,912 km² (738 sq mi), with a drainage basin a little over double that, about 4,503 km² (1,739 sq mi). The deepest known point, located to the south of the island of Visingsö, is 128 meters (420 ft). The average depth is 41 meters (135 ft). The lake has a perimeter of about 642 km (399 mi). The volume is 77.0 km³ (18.5 cu mi). 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 basin is still covered with spruce, pine and deciduous forest. About 26.7% is dedicated to agriculture.

While many of smaller lakes in southern Sweden are thought to have originated by glacial stripping of an irregular weathering mantle in the last 2.5 million years Vättern formed by tectonics as a graben 700 to 800 million years ago in the Neoproterozoic. Granitic basement rocks in the lake are deformed (foliated) by the Protogine Zone that crosses the area. The basin is partially filled by sedimentary rock of the Visingsö Group of Neoproterozoic age. This group include rocks such as conglomerate, sandstone, arkose and carbonates. The older of these sediments deposited before the Vättern came into existence as a graben. Acritarch microfossils such as Chuaria circularis are common in Visingsö Group.

During the most recent millions of years multiple glaciations have covered the lake and its surroundings, leaving glacial striations and drumlins as they receded.