Vänern

Vänern 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. With its surface located at 44 m with a maximum depth of 106 m, the lowest point of the Vänern basin is at 62 m below sea level. The average depth is at a more modest 28 m, which means that the average point of the lake floor remains above sea level.

Vänern drains into Göta älv towards Gothenburg and the Kattegat opening strait between the Atlantic Ocean’s North Sea and the Baltic Sea (It is the only one of the ten largest lakes in Sweden not to drain out to the eastern coastline. The Göta Canal built in the 19th century formd a waterway that runs to Vättern wholly rising when proceeding eastward, and then a navigable river linking the east coast with Vänern. The main inflow of water comes from Klarälven entering Vänern near Karlstad with its source in Trøndelag in Norway.

History
The southeastern part of the Vänern is a depression that appears to have come into being by erosion of Paleozoic-aged sedimentary rock during the Quaternary glaciation that reached to the area. This erosion would have re-exposed parts of the Sub-Cambrian peneplain. Because the southern and eastern shores are parts where the Sub-Cambrian peneplain gently tilts towards the north and west, respectively, the lake is rather shallow at these places. The western shore of the lake largely follows a fault scarp associated to Vänern-Göta Fault.

The modern lake was formed after the Quaternary glaciation 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 fact that ensuing post-glacial rebound surpassed concurrent sea-level rise, lake Vänern became a part of the Ancylus Lake that occupied the Baltic basin. Vänern was connected to Ancylus Lake by a strait at Degerfors, Värmland. Further uplifting made lakes such as Vänern and Vättern become cut off from the Baltic. As a result, there are still species remaining from the ice age not normally encountered in freshwater 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 Mälaren was probably originally about Vänern: the Swedish king Gylfi promised a woman, Gefjon, 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. The Prose Edda says that 'the inlets in the lake correspond to the headlands in Zealand'; since this is much more true of 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, Vänern is stated to be near the location of the dragon's mound at Earnaness.

Geography


Vänern covers an area of 5655 km2, approximately twice the surface area of Luxembourg. Its surface is 44 m above sea level and it is on average 27 m deep. The maximum depth of the lake is 106 m The water level of the lake is regulated by the Vargön Hydroelectric Power Station.

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 Vänern offers are illustrated by the surrounding towns, which have supported 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 Vänern. It has the best view over the lake (about 270 m above the lake level). Another nearby mountain is Halleberg.

Environment


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.

Some bays also have problems with eutrophication and have become overgrown with algae and plant plankton.

Fish
Vänern has many different fish species. Locals and government officials try to enforce fishing preservation projects, due to threats to the fish habitat. These threats include water cultivation in the tributaries, pollution and the M74 syndrome. Sport fishing in Vänern is free and unregulated, both from the shore and from boats (with some restrictions, e.g. a maximum of three salmon or trout per person per day). Commercial fishing requires permission.

In the open waters of Vänern, the most common fish is the smelt (Osmerus eperlanus), dominating in the eastern Dalbosjön, where the average is 2,600 smelt per hectare. The second most common is the vendace (Coregonus albula), also most prominently in Dalbosjön, with 200–300 fish per hectare. The populations may vary greatly between years, depending on temperature, water level and quality.

The most important large fish in the lake are brown trout (Salmo trutta) and zander (Sander lucioperca). The most important small fish is the stickleback.

Vänern has five distinguished species of whitefish:
 * Coregonus pallasii (also common in Neva, Gulf of Finland, Baltic Sea)
 * Lacustrine fluvial whitefish (Coregonus megalops)
 * Coregonus maxillaris (population mainly known around Sweden)
 * Coregonus nilssoni
 * Valaam whitefish (Coregonus widegreni)
 * Coregonus maxillaris

Birds


The most common birds near Vänern are terns and gulls.

Great cormorants have returned and are flourishing. This has contributed to the increase in the population of white-tailed sea eagles, who feed on cormorants.