The fish in the lake
Lake Þingvallavatn is no exception, and in the lake there live three of the five species of freshwater fish found in Iceland: brown trout, Arctic charr and the three-spine stickleback. It’s said that these fish became isolated in the lake in the wake of the last ice age when the terrain rose at the south end of Þingvallavatn.
These three species are a living testimony to how the evolution of species occurs in nature, as over a period of 10,000 years they have adapted themselves to various habitats in the lake. The constant, regular influx of groundwater into Lake Þingvallavatn, together with a very varied habitat, has created good conditions for fish and other life forms in the lake, to which they have adapted even more.
Such evolution is reflected in the different types of Arctic charr and stickleback, along with varying populations of brown trout. Because of this, Þingvallavatn has recently become a focus of research activity on the first stages of variety and species formation.
We offer fishing trips for lake Thingvellir
THE BROWN TROUT
The brown trout in Lake Þingvallavatn, whose origin can be traced to Britain, has long been one of the most talked-about freshwater fish in Iceland – and abroad. The brown trout’s fame is based primarily on its large size and great numbers. After it became isolated in Þingvallavatn in the wake of the last ice age, living conditions proved beneficial, and it was found in many populations all over the lake.
The best-known population was connected with Efra-Sog, which was the natural output of Þingvallavatn to the south, while another well-known population still has its spawning site in the river Öxará. The main reasons why the lake’s largest brown trout population stayed in Efra-Sog were the strong current and river gravel that created good conditions for spawning and for the development of black flies, a good food source.
The brown trout can reach an incredible size, that once attracted anglers from all over the world. Records show that it wasn’t uncommon to catch a 20-30 pound brown trout. When the Steingrímsstöð hydroelectric plant was built in 1959 at the southern end of the lake, the largest spawning site of the brown trout was destroyed, and the largest brown trout population in the lake has yet to recover.
Recently, the life habits of the brown trout have been researched in detail in order to learn more about this lake giant. During this research, brown trout up to 20 pounds in weight have been observed in the river Öxará.
In one respect Lake Þingvallavatn is unique in the world, since it supports four separate varieties of the Arctic char. The Arctic charr in Lake Þingvallavatn are a good example of how species evolve and adapt to their surroundings, as these four varieties have evolved from one species in only 10,000 years.
The Arctic charr, or bleikja, have adapted themselves to two main lake habitats, the main body of water and the bottom of the lake. In the main body of the lake, the food source of the Arctic charr is constantly on the move and the fish themselves have little shelter from predators. The Arctic charr that have evolved under these conditions are streamlined and have a long lower jaw.
The fish-eating type, the Sílableikja (piscivorous charr), can grow up to 40 centimetres in length, while the plant-eating Murta (planktivorous charr) is a lot smaller, usually only about 20 centimetres in length.The lake bottom is the main habitat of the large snail-eating charr and the dwarf-charr. There is enough food there and also plenty of places to hide from predators. The snail-eating charr can be up to 50 centimetres in length, while the dwarf-charr stands up to its name and is usually only 10-13 centimetres. The dwarf-arctic charr can often be seen in the Flosagjá fault (Money rift), where it darts among the coins that tourists throw in the rift.
THREE SPINE STICKLEBACKS
Sticklebacks have adapted themselves to their surroundingsin the same way as Arctic charr, as 2 varieties of stickleback have evolved. One variety stays in the vegetation belt at a depth of 25-30 metres, where a suitable habitat is found, while the other frequents shallower areas amongst the lava stones. Sticklebacks are by far the most common fish in the lake; their number estimated at 85 million.
An old Icelandic proverb says “Fertile is water that runs under lava.” The proverb is particularly appropriate for the water that flows into Lake Þingvallavatn. The close relationship between the ecosystem of Lake Þingvallavatn and geological history gives Þingvallavatn a special place amongst the
The Lake – Nature
The majority of the catchment area is covered by lava and water easily drains through. The young age of the lava means that there is a high uptake of minerals in the groundwater, and this is one of the reasons for the great diversity of life in Þingvallavatn. Land subsidence, rifting and lava have created a diverse habitat, for instance hideouts for fish in fissures and holes along the shoreline.
The lake is particularly fertile and rich in vegetation, despite the very cold temperatures. A third of the bottom area is covered by vegetation, and there is a large amount of algae. Low-growing vegetation extends out to a depth of 10 metres while higher vegetation forms a large growing-belt to 10-30 metres deep.
A total of 150 types of plants have been found and 50 kinds of invertebrates, from the shore to the center.