Vransko jezero (Vransko Lake) is the largest natural lake in Croatia and represents a geomorphological rarity of our karst area since it is a cryptodepression filled with mildly salt water in which a specific community of sea organisms developed.
The north-western part of the lake is in the zone of intensive flooding and is designated a special ornithological reserve due to its diversity of bird species (wetland birds). The Park currently records 235 bird species, of which 102 are nesting birds, while for others the Park is an important wintering or transitory site. The total of 75 different bird species use Vransko Lake as their wintering grounds with more than 200,000 birds, which makes it one of the most important European wintering grounds. As much as 143 migratory bird species from Central and North Europe use this area as resting grounds before continuing their journey. Because of all of the above, in 1983 Vransko Lake was included in the List of European Important Bird Areas (IBA). The Park’s biological value is enhanced by its wealth of fish, if which the presence of a Mediterranean subspecies of common rudd.