Lake Mývatn is the country's fourth largest natural lake, with an area of about 37 square kilometres. Numerous bays and creeks incise its coastline and the lake comprises some fifty islands and islets. The lake is not very deep, its average depth being 2.5 metres, and the maximum depth is 4 metres. The ecosystem of Lake Myvatn is unique. The lake derives its name from the profusion of midges that pervade the area. Bird life is extremely diverse and more species of duck are believed to live around Lake Myvatn than anywhere else in the world.