Karst Rivers | Natural Heritage of Serbia

Nature often hides unusual places and phenomena that inspire explorers, fuel imagination, and call for adventure. One such phenomenon is underground rivers - sinkholes, most commonly hidden in hard-to-reach areas of our planet. In Greek mythology, they symbolized the entrance to the underworld, and even today, in some nations and cultures, they are considered mystical places.

As their name suggests, sinkholes are rivers that disappear into the depths of the Earth's surface, and the places where this happens are called sinkholes, abysses, or pits. They are typical for karst terrains made of water-permeable rocks. These terrains are rich in caves and caverns through which, far below the surface, underground rivers used to flow. To make the phenomenon even more intriguing, these rivers sometimes resurface as powerful springs, such as the Krupaja Spring, Mlava Spring, Crni Timok, Svrljiški Timok, and others.

In Europe, there are not many sinkholes, but the most famous one is, believe it or not - the Danube River! At the beginning of its course, in the Schwarzwald region, a part of the Danube's water flows underground and then resurfaces not far from Lake Constance. During the summer, it happens that the Danube's riverbed on that section briefly remains without water, and in Germany, this phenomenon is called "the disappearance of the Danube."

There are many karst terrains on the Balkan Peninsula, so sinkholes are a common occurrence in Bosnia and Herzegovina, Croatia, Slovenia, and Montenegro. The most famous sinkholes in these regions are the Reka in Slovenia, which disappears in the Škocjan Caves, as well as the Lika and Gacka rivers in Croatia, the Trebišnjica River in Bosnia and Herzegovina, and others. We are certainly most interested in sinkholes that occur within the borders of our country.

In Serbia, sinkholes occur in areas made of limestone rocks. The largest number of sinkholes is found in the Carpathian-Balkan mountains in eastern Serbia (Kučaj, Beljanica, Miroč, Homolje Mountains...), where there are about seventy registered underground watercourses. They are mostly shorter underground streams, but there are also those that wander for kilometers through the underground before they emerge on the surface.

One of the most picturesque karst areas in Serbia is the Dubašnica Plateau, on the eastern slopes of the Kučaj Mountains. Thanks to porous rocks, this area represents an extremely dry environment, especially in the summer months when all the water from the surface drains through underground watercourses. The largest cave in Serbia, Lazareva Cave, is largely formed by the waters that sink from the Dubašnica Plateau.

The most famous sinkholes in this region are Dubašnica, Demizlok, Mikuljska river, and Vojal. These rivers mostly flow underground and emerge from several caves as powerful springs. Only during rainy periods does their water flow on the surface, while for most of the year, they wander through the depths of limestone massifs. These four rivers have carved magnificent canyons in the past, which are now eagerly visited by hikers and nature lovers. In Kučaj, there are many seasonal sinkhole rivers that occur mainly during the rainy periods of the year.

Beljanica is a mountain in Eastern Serbia, stretching between Žagubica, Krepoljin, and Despotovac. This limestone mountain hides numerous speleological objects (caves and pits) and sinkholes. The most famous ones are Rečka and Busovata. Busovata is one of the largest sinkholes in Serbia, approximately 9 km long, and the sinkhole through which Rečka disappears underground is one of the deepest in our country (Ivkov sinkhole, about 150 m deep).

River sinking or at least parts of their water also occurs in larger rivers. Turija River is one of the source branches of the Svrljiški Timok, which, after a surface flow of about ten kilometers, reaches the Pandiralo sinkhole and after only 600 meters of underground drainage, emerges again on the surface at the spring of Svrljiški Timok. It often happens that a small lake forms where the water sinks because underground channels cannot absorb all the water. Further downstream, Svrljiški Timok passes through one of the most beautiful gorges in Serbia.

Berovička River is one of the most interesting sinkholes in Eastern Serbia. It is located near Pirot, in the Nišava watershed. It emerges from the eponymous lake formed only during rainy periods. When the lake reaches a certain surface area, the Berovička River is created, which springs from the lake and quickly disappears underground. After two kilometers of underground flow, its waters emerge in the Jerma River canyon. Near Dimitrovgrad, there is also the sinkhole Blato, which springs from the eponymous lake and then sinks into the Popova Cave.

The surroundings of Valjevo are abundant in limestone rocks and, consequently, sinkholes. On Maljen, Povlen, and Medvednik, which form a horseshoe shape around Valjevo, there are a large number of sinkholes. The most famous ones are Gradac, Polička, Povlenska River, Plandište, Koljanica, Radmilovac, and others. The Gradac River springs at the foot of Povlen, quickly sinks into the depths, and then emerges not far from the village of Bogatić. From that point to Valjevo, Gradac creates one of the most beautiful gorges in Serbia, which is also a favorite excursion spot for the people of Valjevo.

There are also limestone terrains in southwestern Serbia. On the Pešter Plateau, the largest sinkhole in Serbia is located – the Boroštica River. After a surface flow of 18 kilometers, this river sinks below the Pešter field and flows underground for 12 kilometers before its waters finally emerge at the Juriška Springs in Montenegro. In addition to Boroštice, there are several shorter sinkholes on Pešter, and some of them are Crna River, Delimeđska, and Točilovska River.

Depending on weather conditions, some of these sinkholes can be seen throughout the year, but the majority of them occur only during the rainy seasons when, admittedly, the conditions for mountain walks are not optimal. However, with a little effort and patience, carrying a backpack, wearing good footwear, and having a raincoat (just in case), you can witness this extremely interesting natural phenomenon throughout Serbia.