Cerknica Lake – Lake that vanishes

The intermittent Lake Cerknica that can cover up to 26 km² of the Cerknica Polje at times of high water. Photo: UKOM archive

In the heart of Notranjska, the most distinct Karst landscape in Slovenia, in a Karst field sheltered from the southwest by the densely wooded Javorniki Hills, lies the illustrious Cerknica Lake. It is an intermittent lake, filled mainly by autumn rains and the early spring thaw, which stops in May or June, sometimes even in mid-winter. The water comes from Karst springs bubbling up at the Lake’s edge and flows out underground, through sinkholes. Its surface level varies by over 7 metres (it lies between 546 and 553 metres above sea level). When the water is low, it spans over 20 square kilometres, but when high waters set in, it is over 10 kilometres in length, almost 5 kilometres wide, and its surface area exceeds 30 square kilometres.

The most interesting phase in the Lake's annual cycle is when it fills up.

The constantly changing landscape. Photo: UKOM archive

Lake Cerknica can cover up to 26km² of the Cerknica Polje at times of high water

The most interesting phase in the Lake's annual cycle is when it fills up.

Water starts bursting from vent holes and the streams rise immediately, flooding the field at the bottom of the valley. When it starts receding, the water disappears into picturesque sinkholes and into swallow-holes, entrances to the hollow Karst underground which is embellished with stalagmites and stalactites.

Some of the outflow water resurfaces at Močilnik, the source of the Ljubljanica River. Cerknica Lake is an important fish habitat, as well as a nesting ground for many species of bird. It is increasingly popular as a recreational area, ideal for fishing, hiking, nature excursions (speleology), wind-surfing, swimming, and ice-skating – depending on the season and the water level. The constantly changing landscape makes it worth a visit in any season.

Fame to the Lake, membership of the Royal Society

Cerknica Lake is an important habitat for many species of bird. Photo: UKOM archive

Stories about the miraculous Lake have for centuries inspired artists, in whose imaginations it acquired a sense of the divine and unfathomable; Dante Alighieri saw it in this way in his Divine Comedy. The lake became known globally when the intermittence mechanism was first described over 300 years ago by the Slovene polymath, historian, topographer, ethnographer and sketcher, Baron Janez Vajkard Valvasor (1641-1693), which earned him membership of the Royal Society. He also published a lengthy summary of his description in his most comprehensive work, The Glory of the Duchy of Carniola.