What is "leirvogsvatn"

Leirvogsvatn is a small lake, located about 23 kilometres northeast of Reykjavík, Iceland. It lies along Route 36. Located at 211 metres above sea level, it has an area of 1.2 km² with a maximum depth of 16 metres. Fed by the Leirvogsvatn River, the lake is the subject of a legend in the form of a horse-shaped monster. The lake is known to contain populations of Gasterosteus islandicus.