Lake Cerknica

Lake Cerknica, or Cerkniško jezero, lies in a broad karst basin between the Notranjska hills in southwestern Slovenia and is often described as the largest intermittent lake in Europe, a distinction that makes it one of Europe’s natural curiosities and one of Slovenia’s best known landscapes. It does not behave like an ordinary lake. The basin is surrounded by limestone, and the water that drains into it from rivers and springs also leaves through a series of underground channels and swallow holes known as ponors. When rainfall or snowmelt exceeds what the ponors can swallow, usually in autumn and spring, the basin fills with water and can cover many square kilometres. When the weather turns dry in summer, the water sinks away, sometimes within a few days, and the lake bed turns into wet meadows and then grass.

Few places show the idea of a karst landscape so clearly, and that is why the lake has attracted attention for centuries. The Carniolan scholar Janez Vajkard Valvasor described the lake in the late seventeenth century, and his account helped bring its odd rhythm to the attention of scientists elsewhere in Europe. Local folklore has its own explanations, and stories about the water's sudden coming and going are still told around the shore.

What you see depends entirely on the season. In a full lake year you can paddle a small boat between the reeds, watch fishing and enjoy the quiet surface under the surrounding hills. In winter the surface can freeze and skaters take to the ice. When the water has drained, farmers cut hay on the bed, and walkers and cyclists can follow tracks across ground that was underwater a few weeks earlier. The area is also known for birds, and the wetlands hold breeding and migrating species, amphibians and rare plants, which is part of why it has been protected as a wetland of international importance. Binoculars are worth bringing.

Nearby, the Visitor Center by the lake is a good first stop. It can explain the hydrology, suggest routes and help with boat or bike hire. The lake itself has no entrance gate, but it covers a large area and paths are scattered around the shore, so ask locally about which part is accessible at the time of your visit.

It suits nature lovers, photographers, families and slow travellers, and it works well as part of a wider trip with Postojna Cave and Predjama Castle, which are both within reach by car. Visit more than once if you can, because spring and autumn show a very different place from high summer.