Lake, no lake. These intermittent lakes fill with water mostly in the autumn, and drain away in the spring. Although the lakes are certainly fascinating regardless of the season. When full of water, they are especially magical, but when dry, they turn into magnificent, densely populated pastures, or into “dry pictures” with cracked and parched surfaces. Lake Cerknica is Europe’s largest intermittent lake and inspires visitors through its diverse fauna and flora, as well as countless natural landmarks. The River Pivka, when water fills the lower smaller and larger hollows, forms seventeen intermittent lakes. In the Municipality of Ilirska Bistrica, the artificial lakes Klivnik and Mola can be found.
The Intermittent Lake Cerknica. Due to its regular draining and filling, it had already attracted explorers as early as in the 17th century, and has been the object of study and admiration ever since. The vast lake reed beds provide shelter, food, and nesting grounds to a variety of water and other birds. The lake is a nesting ground for 94 different species, although more than 230 species have been observed in its vicinity. These species include endangered and rare Slovenian and European birds (Corn Crake Crex Crex, Red-necked Grebe Podiceps grisegena, Common Redshank Tringa totanus, Great Crested Grebe Podiceps cristatus, Little Grebe Tachybaptus ruficollis, Eurasian Curlew Numanius arquata, and others). For the variety of water and wading birds, Lake Cerknica is one of the most important Slovenian nesting grounds; it is a rest area for many migrating birds, and also a wintering area for others. This makes Lake Cerknica an important ornithological location. In summer, Lake Cerknica is usually completely drained. When the water level drops, deep sinkholes are exposed underneath a thick layer of sediment. This largest Slovenian karst plain is a real tourist magnet regardless of the season.
The Pivka Lakes
Beside the River Pivka and its many tributaries, the Pivka basin has also been rewarded by nature with numerous karst formations-on the surface, many springs and resurgences appear, which fill small and large hollows alike, forming seventeen intermittent lakes, which are always a spectacular sight. During dry periods, a vast grass-covered lake bottom surfaces, though when filled with water, the lake emanates a certain mysterious beauty, and especially in winter, its icy surface sets a magical winter mood. Among the lakes, two are the biggest and most long-lasting – Lake Petelinje and Lake Palčje. After rainfall, they remain full for several months, and in dry periods, the lakes’ waters are lost into the underground, and the lake bottoms are covered by grass, which is also cut by the locals. In dry periods and especially during summer, the lake bottoms turn into vast pastures, and are the perfect hiking destination, particularly for flora and fauna enthusiasts.
Lake Palčje is the biggest lake of the Pivka Basin. It is located north of the village of Palčje, in a 2.5km long and 0.5km wide karst hollow and has a levelled and deposited bottom. Lake Palčje filling and draining patterns change every year. Similarly to other intermittent lakes, Lake Palčje’s existence depends on the quantity and annual allocation of rainwater, though the lake is usually full at least nine months during the year. The bottom of the dry Lake Palčje is covered with pastures and willows. The willows are an important nesting ground for many bird species, especially Warblers, Red-backed Shrikes, and Corn Buntings. Nests of these birds in Lake Palčje are more common than anywhere else in Slovenia. Approximately half of all nesting birds in the Pivka basin have been classified in the Red List of endangered species of Slovenia. Among them is the Corn Crake, which is globally endangered due to the constant reduction of wet pastures. The fact that over half of all Slovenian butterflies can be found around the Pivka Lakes is a testament to its exquisite biotic diversity. It has been recorded that the grasslands of Lake Palčje are the home of as many as 70 species, while 88 butterfly species inhabit all of the lakes. When the lakes drain in spring, the lake bottom is covered in colourful carpets.
Lake Petelinje is the second largest River Pivka lake after Lake Palčje, and is the most long-lasting one, since it is filled up to half a year annually – it fills in spring, starting April, and does not drain until the beginning of the dry period, sometimes not until autumn. When the waters are at their highest, the lake has a maximum depth of 5–7m and a surface area of 55ha. Due to annual draining and lack of connection to other waters, no fish inhabit the lake. Special attention should be given to a 5mm crab, as today, it can only be found living in Lake Petelinje.
Near the Volčje Village, the locals have tidied the surroundings of Lake Bloke. In the summer, the lake attracts swimmers, and in winter, the frozen surface is irresistible to ice skaters. Almost throughout the year, though, fishermen can be seen dipping their baits into the lake, hoping to catch a large Carp, Trout, or Common Rudd. The beautiful and pleasant surroundings, warm lake water, and shallow marshes are a guarantee of a pleasant stay.
The Klivnik and Mola are artificial lakes in the Brkini Hills. Lake Mola lies on the eastern edge of the central Brkini Hills ridge, below the Harije Village. Its size is substantial, and has a very active network. The lake serves as protection from high waters and is an important water source in dry periods. It is also used for aquafarming and fishing. Lake Klivnik is the result of the dammed Klivnik River, southeast from the elongated and the clustered Tominje Village. To the east, the stretched Brkini Hills ridges rise, while the southern edge of the lake borders on the hilly forest areas of Zavrh. The lake protects the nearby villages in case of high as well as low waters. It is also intended for orchard irrigation, as well as aquafarming and fishing.