The intermittent Lake Cerknica is a unique karst phenomenon appearing at the bottom of the Cerknica polje karst depression. It is characterised by extreme inter-annual water level fluctuation. Part of the year the area is flooded, but in summer, it dries up. The lake has been exciting the imagination of local people and visitors for centuries. Many of them believed that the lake is appearing and disappearing due to magic powers. In the 17th century the opinion that intermittence was enabled by a system of underground lakes interconnected with the system of siphons was prevailing. In the 18th century Nagel and Gruber came to a simple conclusion that the lake appears as a consequence of a surplus of water in the area. The first detailed written information on the lake dates back to 1679, when Slovenian polymath J. V. Valvasor, a member of the English Royal Society, published an essay on the lake. Due to this publication and many others describing the outstanding ecosystem, the lake became famous across all over the world.
»Lake« in the dry period (left) and flooded (right) (Archive of the Notranjska Regional Park).
The Rakov Škocjan valley is a karst valley at the northern foot of the Javorniki hills, which was created by collapsing of the ceiling of a karst cave. The remains are the Small and the Great Natural Bridge, which are 37 and 42 m high, respectively. The Rak river stream meanders at the bottom of the valley, surrounded by forests and wet meadows. The Rak is supplied by underground waters discharging from the Cerknica polje and from the Javorniki hills. This small river origins in the Zelške caves in the eastern part of the valley, and sinks into the Tkalca cave in the west.
Together with Lake Cerknica and the Križna cave, the Rakov Škocjan valley has been designated as a wetland of international importance – Ramsar Site. This valley was also the first Slovenian regional park, established as early as 1949.
Small (left, middle) and Great Natural Bridge (right) (Archive of the Notranjska Regional Park).