The Ohrid lake is one of the largest biological reserves in Europe, possessing unique flora and fauna which are extinct elswere. Only Lake Ohrid, Lake Tanganyka, Lake Caspi, and Lake Baikal are believed to have been formed during the Tertiary Period some 2-4 million years ago, and hence these lakes are characterized by unique flora and fauna distinct to that period. Due to its age, many of Lake Ohridís aquatic species are endemic including ten of the seventeen fish species. In addition, there are five particular endemic species which are restricted to small areas of the Lake such as special various birds, as well as four fish spawning grounds. Because of its rich history and unique flora and fauna, Lake Ohrid was declared a UNESCO World Cultural and Natural heritage Site in 1980.