from Hjortens Udde
Detail map of the lake with surroundings
|Primary outflows||Göta älv|
|Surface area||5,650 km²|
|Average depth||27 m|
|Max. depth||106 m|
|Water volume||153 km³|
|Surface elevation||44 m|
|Islands||Brommö, Djurö, Fågelö, Hammarö, Kållandsö, Lurö|
Vänern (Swedish pronunciation: [ˈvɛːnəɳ]) is the largest lake in Sweden, the largest lake in the European Union and the third-largest lake in Europe after Ladoga and Onega in Russia. It is located in the provinces of Västergötland, Dalsland, and Värmland in the southwest of the country.
Geologically, the lake was formed after the last ice age about 10,000 years ago; when the ice melted, the entire width of Sweden was covered in water, creating a strait between Kattegat and the Gulf of Bothnia. Due to the ensuing isostatic rebound, lakes such as Vänern and Vättern became pursed off. As a result, there are still species remaining from the ice age not normally encountered in fresh water lakes, such as the amphipod Monoporeia affinis. A Viking ship was found on the lake's bottom on May 6, 2009.
A story told by the 13th-century Icelandic mythographer Snorri Sturluson in his Prose Edda about the origin of Lake Mälaren was probably originally about Lake Vänern: the Swedish king Gylfi promised a woman, Gefjun, as much land as four oxen could plough in a day and a night, but she used oxen from the land of the giants, and moreover uprooted the land and dragged it into the sea, where it became the island of Zealand. Snorra Edda says that 'the inlets in the lake correspond to the headlands in Zealand'; since this is much more true of Lake Vänern, the myth was probably originally about Vänern, not Mälaren.
The Battle on the Ice of Lake Vänern was a 6th-century battle recorded in the Norse sagas and referred to in the Old English epic Beowulf. In Beowulf Lake Vänern is stated to be near the location of the Dragons mound at Earnanæs.
Geographically, it is situated on the border between the Swedish regions of Götaland and Svealand, divided between several Swedish provinces: The western body of water is known as the Dalbosjön, with its main part belonging to Dalsland; the eastern body is known as Värmlandsjön, its northern part belonging to Värmland and the southern to Västergötland.
Its main tributary is Klarälven, which flows into the lake near the city of Karlstad, on the northern shore. Other tributaries include Gullspångsälven, Byälven and Norsälven. It is drained to the south-west by Göta älv, which forms part of the Göta Canal waterway, to Lake Viken into Lake Vättern, southeast across Sweden.
The economic opportunities Lake Vänern offers are illustrated by the surrounding towns, which have supporting themselves for centuries by fishing and allowing easy transportation to other cities or west by Göta älv to the sea of Kattegat. This directly includes: Karlstad (chartered in 1584), Kristinehamn (1642), Mariestad (1583), Lidköping (1446) Vänersborg (1644), Åmål (1643), Säffle (1951), and indirectly Trollhättan (1916).
The Djurö archipelago surrounds the island of Djurö, in the middle of the lake, and has been given national park status as Djurö National Park.
The ridge (plateau mountain) Kinnekulle is a popular tourist attraction near the south-eastern shore of Lake Vänern. It has the best view over the lake (about 270 metres (890 ft) above the lake level). Another nearby mountain is Halleberg.
Environmental monitoring studies are conducted annually. In a 2002 report, the data showed no marked decrease in overall water quality, but a slight decrease in visibility due to an increase of algae. An increasing level of nitrogen had been problematic during the 1970s through 1990s, but is now being regulated and is at a steady level.
Lake Vänern has many different fish species. Locals and government officials try to enforce fishing preservation projects, due to various threats to the fish habitats. These threats include water cultivation in the tributaries, pollution and the M74 syndrome. Sport fishing in Lake Vänern is still free and unregulated, both from the shores and from boats (with some restrictions, e.g. a maximum of three salmon or trout per person per day). Only commercial fishing requires permission.
In the open waters of Lake Vänern, the most common fish is the smelt, dominating in the eastern Dalbosjön, where the average is 2,600 smelt per hectare. The second most common fish is the vendace (Coregonus albula), also most prominently in Dalbosjön, with 200–300 fish per hectare. The populations may vary greatly between years, though, depending on temperature and the water level and quality.
The fish in Lake Vänern are important for the industry of the towns around it. In 2001, 165 tons (165,000 kg) of vendace, 100 tons of whitefish, and 25 tons of eel were caught.
Lake Vänern has two sub-groups of lake salmon known as Vänern salmon. They are native to Lake Vänern and spawn in the adjacent lakes. The first sub-group is named after the eastern tributary Gullspångsälven as the Gullspång salmon. The second is the Klarälv salmon, mainly spawning in the Klarälven. These sub-groups are related to Baltic Sea salmon, and they have developed in Lake Vänern for over 9,000 years. They are notable in that they have never entered the ocean.
These large lake salmon are known to weigh some 18 kilograms (40 lb); the world's largest lake salmon, exceeding 20 kilograms (44 lb), was caught in Lake Vänern. There are also three other species of salmon-like fishes in the connecting rivers.
Other fish 
Vänern has five distinguished species of whitefish:
- Coregonus pallasii (also common in Neva, Gulf of Finland, Baltic Sea)
- Lacustrine fluvial whitefish (Coreganus megalops)
- Coreganus maxillaris (population mainly known around Sweden)
- Coregoni nilssoni
- Valaam whitefish (Coreganus widegreni)
- Coregonus maxillaris
Cormorants vanished in the 19th century, but have since returned and are flourishing. This has contributed to the increase in the population of sea eagles, who feed on cormorants. However, fishermen are not so happy, as cormorants raid their nets.
- Seppälä, Matti (2005), The Physical Geography of Fennoscandia, Oxford University Press, p. 145, ISBN 978-0-19-924590-1
- Anthony Faulkes (ed. and trans), Snorri Sturluson: Edda (London: Everyman, 1987), p. 7.
- Heimir Pálsson, 'Tertium vero datur: A study of the text of DG 11 4to', p. 44 http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-126249.
- World Lakes Database