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.