Lake Cerknica (Cerkniško jezero) is one of the largest intermittent lakes in Europe. It appears every year in the karst polje bounded by the Javorniki hills, the Bloke Plateau and Slivnica. In the dry part of the year the lake disappears, meaning that in the space of a year you can row, fish, walk and mow grass – all in the same place!
Water usually remains on the polje for around nine months of the year. In normal conditions the lake covers an area of more than 20 km2, but when water levels are highest this figure increases to almost 30 km2. When it is full, Lake Cerknica is the biggest lake in Slovenia.
The importance of the intermittent Lake Cerknica thus far exceeds the borders of Slovenia. Lake Cerknica, along with the Rakov Škocjan valley and the cave Križna Jama, has been proclaimed a wetland of international importance under the
Ramsar Convention and a
Natura 2000 area because of its importance for endangered bird species.
The biodiversity in this area is truly remarkable. Species observed here include 276 birds – half of all European species; 45 mammals – half of all European species; 125 butterflies – just under a third of all European species; and 15 amphibians – almost a quarter of all European species.