Lake Thingvallavatn is the largest „natural” lake of the country with an area of 83,7 km².
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.
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.