Mývatn (Mivatn) is a famous lake situated in an area of active volcanism in the north of Iceland. The lake and its surrounding wetlands have an exceptionally rich fauna of waterbirds, especially ducks. The lake was created by a large lava eruption about 2300 years ago, and the surrounding landscape is dominated by volcanic landforms, including lava pillars and rootless vents. The effluent river Laxá (Laxa) is known for its rich fishing for brown trout and Atlantic salmon.
The name of the lake comes from the huge numbers of midges to be found there in the summer.
The name Mývatn is sometimes used not only for the lake but the whole surrounding inhabited area. The River Laxá, Lake Mývatn and the surrounding wetlands are protected as a nature reserve.
Lake Mývatn was created about 2300 years ago by a large fissure eruption pouring out basaltic lava. The lava flowed down Laxárdalur Valley to the lowland plain of Aðaldalur where it entered the Arctic Ocean about 50 km away from Mývatn. The crater row that was formed on top of the eruptive fissure is called Þrengslaborgir (or Lúdentarborgir) and has often been used as a textbook example of this type of volcanic activity. There was a large lake in the area at the time, a precursor of the present-day Mývatn. When the glowing lava encountered the lake some of the water-logged lake sediment was trapped underneath it. The ensuing steam explosions tore the lava into small pieces which were thrown up into the air, together with some of the lake.
By repeated explosions in a number of locations, groups of craters built up and now dominate the landscape on the shore of Lake Mývatn and also form some of the islands in the lake. This type of lava formation is known as pseudocraters or rootless vents. A group of such craters at Skútustaðir on the south shore of the lake is protected as a natural monument and is frequented by tourists. Other pseudocrater groups in this lava field are in the Laxárdalur Valley and Aðaldalur. The formation of pseudocraters halted the advance of the lava in some places creating temporary lava lakes. The lava eventually drained from the lakes, leaving behind a forest of rock pillars. The biggest of these formations is named Dimmuborgir. At another place, Höfði, the pillars stand in the lake water. The lava created by the Þrengslaborgir eruption is known as the Younger Laxá Lava.
The Mývatnseldar eruptions and volcanic activity near Krafla in 1975-1984 was characterized by periods of slow land rise, interspersed by shorter periods of rapid subsidence, underground magma bursts, rifting, earthquakes and eruptions (nine in all). This is an excellent example of the process of continental drift in Iceland. A central volcano and its associated fissure swarm is called a volcanic system. The Krafla volcanic system is one of several such systems which together form the volcanic zone of Iceland.
The lake is fed by nutrient-rich springwater and has a high abundance of aquatic insects that form the food supply for ducks. Thirteen species of ducks nest here. Most of the ducks are migratory, arriving in late April – early May from north-western Europe. Other common waterbirds include the Slavonian grebe, red-necked phalarope, great northern diver, red-throated diver and whooper swan.
The waterbird situation has been monitored annually since 1975 by the Mývatn Research Station. There is a long tradition of harvesting duck eggs for home use on the local farms. To ensure sustainability, the harvesting follows strict age-old rules of leaving at least four eggs in a nest for the duck to incubate.