Mývatn is a shallow eutrophic lake situated in an area of active volcanism in the north of Iceland, not far from Krafla volcano. The lake and its surrounding wetlands have an exceptionally rich fauna of waterbirds, especially ducks. The lake was created by a large basaltic lava eruption 2300 years ago, and the surrounding landscape is dominated by volcanic landforms, including lava pillars and rootless vents (pseudocraters). The effluent river Laxá is known for its rich fishing for Brown Trout and Atlantic Salmon.

The name of the lake (Icelandic mý ("midge") and vatn ("lake"); the lake of midges) comes from the huge numbers of flies (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 (The Mývatn-Laxá Nature Conservation Area).

Since the year 2000, a marathon around the lake takes place in summer.

The lake is fed by nutrient-rich springwater and has a high abundance of aquatic insects (Chironomidae) and Cladocera that form an attractive food supply for ducks. Thirteen species of ducks nest here. The duck species composition is unique in the mixture of Eurasian and North American elements and of boreal and arctic species. Most of the ducks are migratory, arriving in late April - early May from north-western Europe. The most abundant is the Tufted Duck, which immigrated to Iceland at the end of the 19th century. The Greater Scaup is the second most common duck species.