right|180px|thumb|Map of Sweden; Vänern in the middle south.Vänern () is the largest
lake in
Sweden and the
third largest lake in Europe. It is located in the
provinces 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, such as the
amphipod Monoporeia affinis. A
Viking ship was found on the lake's bottom on May 6, 2009.
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.
Geographically, it is situated on the border between the Swedish regions of
Götaland and
Svealand, 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.
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 fishermen. There are also three other species of
salmon-like fishes in the connecting rivers.
Other fish
Basically all common fresh water fish are found in Lake Vänern. The most important large fish are
trout and
zander. The most important small fish is the
stickleback.
Vänern has five distinguished species of
whitefish:
Birds
The most common birds near Lake Vänern are
terns and
gulls of different kinds.
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.
Rarer 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.
