Fiskurinn
Relatively very few faunal species are found in Iceland. The main reason is, of course, the distance between Iceland and the mainland, but also the relatively short time since the end of the last Ice Age.
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.
Three species of fish live in lake Þingvallavatn. The largest one is brown trout (Salmo trutta). Then the lake has four morphs of arctic char (Salvelinus alpinus) and a three spined stickleback (Gasterosteus aculeatus L.)
Þingvellir National Park / Gagarín
Benthic charr, Piscivorous charr, Planktivorous charr and dwarf charr are the four morphs of char in lake Þingvallavatn. They have grown to like different habitant area and breeding era. They are though still able to interbreed.
Þingvellir National Park / Gagarín
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.