Vänern

Infobox_lake
lake_name = Vänern
image_lake =Hjortens Udde, lake Vänern Sweden, 2003-04.jpg
caption_lake =from Hjortens Udde
image_bathymetry = Lake Vänern details.pngcaption_bathymetry=Detail map of the lake with surroundings
coords = coord|58|55|N|13|30|E|region:SE_type:waterbody|display=inline,title
type =
inflow = Klarälven
outflow = Göta älv
catchment =
basin_countries = Sweden
length =
width =
area = 5,650 km²
depth = 27 m
max-depth = 106 m
volume = 153 km³
residence_time =
shore =
elevation = 44 m
islands = Brommö, Djurö, Fågelö, Hammarö, Kållandsö, Lurö
cities =
reference = Citation| last=Seppälä| first=Matti| title=The Physical Geography of Fennoscandia | url=http://books.google.com/books?id=q33WekTp7tgC&pg=PA145| publisher=Oxford University Press|date=2005| page=145]

Vänern (IPA: IPA| [ˈvæːnærɳ] ) is the largest lake in Sweden and the third largest lake in Europe. It is located in the counties of Västergötland, Dalsland, and Värmland.

History

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.

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. [ [http://www.ilec.or.jp/database/eur/eur-16.html World Lakes Database] ]

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 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, 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 (plateau 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).

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

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 kilograms) of vendace, 100 tons of whitefish, and 25 tons of eel were caught.Fact|date=February 2007

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.

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) [ [http://www.fishbase.org/Summary/SpeciesSummary.php?id=49240 Fishbase] ]
*"Coregoni nilssoni"
*Valaam whitefish ("Coreganus widegreni")
*"Coregonus maxillaris"

Birds

The most common birds near Lake Vänern are terns and gulls of different kinds.

Cormorants vanished in the 19th century,Fact|date=February 2007 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.

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.Fact|date=February 2007

References

External links

* [http://www.vanern.se/engelsk/eng_index.asp Official site]
* [http://swedentravelnet.com/lake-vanern.html Lake Vanern guide]