Vänern
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| Vänern | |
|---|---|
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| Coordinates | |
| Primary sources | Klarälven |
| Primary outflows | Göta älv |
| Basin countries | Sweden |
| Surface area | 5,650 km² |
| Average depth | 27 m |
| Max depth | 106 m |
| Water volume | 153 km³ |
| Islands | Djurö |
Vänern [IPA: 'vɛːnæɳ] is the largest lake in Sweden and the third largest lake in Europe. It is located in the counties of Västra Götaland and Värmland.
According to Norse mythology, the lake was created by the goddess Gefjun when she tricked Gylfi, the Swedish king of Gylfaginning. The land thusly removed by Gefjun was transported to Denmark, becoming the island of Zealand.
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[edit] History
Geologically, it was formed after the last ice age about 10,000 years ago; when the ice melted, the entire width 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.
[edit] Geography
Lake Vänern covers an area of 5,655 km². It is located at 44 m above sea level and is on average 27 m deep. The maximum depth of the lake is 106 m.[1]
Geographically, it is situated in the area of Götaland, divided into several Swedish provinces: The western body of water is known as the Dalbosjö, with its main part belonging to Dalsland; the eastern body is known as Värmlandsjön, its northern parts 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. It is drained to the south-west by Göta älv, which it forms part of the Göta Canal waterway across Sweden.
The economic opportunities Lake Vänern offers are illustrated by the surrounding towns, having been located there for centuries, supporting themselves 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).
Around the island Djurö, in the middle of the lake, lies the Djurö archipelago, which has been given national park status as Djurö National Park.
The ridge (mountain) Kinnekulle is a popular tourist attraction located near the south-eastern shore of Lake Vänern. It has the best view over the lake (about 270 m above the lake level).
[edit] 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 70s through 90s, 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.
[edit] Fishes
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 and 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 kilograms) of vendace, 100 tons of whitefish, and 25 tons of eel were caught[citation needed].
[edit] Salmon
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 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; the world's largest lake salmon, exceeding 20 kilograms, was caught in Lake Vänern; it is arguably the most desired catch for sport fishers. There are also three other species of salmon-like fishes in the connecting rivers.
[edit] Other fishes
Basically all common fresh water fish are found in Lake Vänern. The most important large fish are trout, bass and zander. 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 (Coreganus megalops)
- Coreganus maxillaris (population mainly known around Sweden) [2]
- Coregoni nilssoni
- Valaam whitefish (Coreganus widegreni)
- Coregonus maxillaris
[edit] Birds
The most common birds near Lake Vänern are terns and gulls of different kinds.
The cormorant vanished in the 19th century,[citation needed] but have since returned and are flourishing. This has contributed to the increase in the population of sea eagles, who feed on the cormorant. However, fishermen are not so happy, as the cormorant raids their nets.
More rare species are the Black-throated diver and the Turnstone (Arenaria interpres), with hardly a dozen nests around Vänern; and the Caspian tern with hardly a dozen specimens.[citation needed]
[edit] External links
| 10 largest lakes in Sweden |
|---|
| Vänern 5,648 km² | Vättern 1,893 km² | Mälaren 1,140 km² | Hjälmaren 484 km² | Storsjön 464 km² | Siljan + Orsasjön 354 km² | Torneträsk 330 km² | Hornavan 252 km² | Uddjaure 210 km² | Bolmen 184 km² |
