»Z vso pravico ga smemo imenovati redkost in pravo čudo narave. Vem, da ni najti ne v Evropi ne v ostalih delih sveta tako čudovitega jezera, kot je to.« Janez V. Valvasor

(“We have every right to name it but a rarity and a real wonder of nature. I know that neither in Europe nor in the rest of the world a lake of such beauty could ever be found.”)   

In the past, the locals have often tried to subordinate the ever changing nature of Cerknica Lake and thus tried to reform it for their own needs. In the 19th century they have tried to dry it out completely and in the industrial era there were tendencies to keep it full of water and build hydroelectric power plant on it.

The lake has been most affected by the drying out regulations in the last few centuries, which had been aimed to reform the lake’s ground for agriculture and livestock breeding. The lake’s flooding had gotten rare and lasted less period of time. There was faster water flow in the channel which had meant that the water carried away more material, the ground water levels had gotten lower. The drainages were taking place despite the government’s prohibition, ignoring even the many locals’ exspressed scuples about it. It had soon become obvious that in many parts the drainages hadn’t brought any of the positive consequences that the people had expected. It was quite the contrary.

Between the years 1844 and 1958 about 12 km of the watercourses Stržen, Goriški Brežiček, Lipsenjščica, Tresenec, and Žerovniščica, which meandered over the lake bottom, were redirected into straight channels. The goal of these interventions was to dry out the lake and obtain more land for agricultural use on the intermittent Cerknica Lake. This goal was not achieved, since the lake soil remained too soaked for the successful growth of crops. The common lenght of the old river-bed in Cerkniško polje was thus reduced by 2 to 3-times. Shorter river-bed means less water which runs off sooner because there is less friction in it. As the consequence, the time of waters staying in the lake, decreases. The swings of Cerknica lake surface levels have become very unpredictable in the last few years and thus unfavourable for fish and for the birds which nest next to the water, as well for the other water organisms.

Nevertheless, these regulations caused harmful changes in natural processes and drastically changed the ecosystem of the intermittent lake. Living conditions of species inhabiting aquatic and riparian habitat types have declined. Some species disappeared from the area entirely. Biodiversity and ecosystem stability was significantly reduced.

The artificial drying of the lake has left other negative consequences:

• faster water flow in the channel means the water carries away more material than it deposits. This leads to the formation of new sinkholes in the watercourse;
• increased erosion of river banks leads to deeper and narrower riverbeds, which is why the water current is getting faster by the year;
• faster water flow and shorter water paths in the straight channels cause reduced self-cleaning ability of watercourses;
• smaller area for the growth of key aquatic plants, which represent hiding places for aquatic animals and where natural water purification takes place;
• overheating of water at low water levels and lower concentration of dissolved oxygen in the water has diminished the living conditions of water organisms;
• less places, suitable for spawning and sheltering fish;
• mineralization of organic matter and increased nutrient content in the soil have changed the conditions in sensitive habitats, such as fens and molinia meadows,
• significant changes in water dynamics prevent the formation of oxbow lakes.

Negative consequences of past interventions, exacerbated by drier summers, caused by climate change, are even more evident nowadays. The lake usually disappears several times a year, instead of once every couple of years, as it used to.

The Notranjska park will give Stržen’s river-bed back its natural double meander in two sections – Ključi and Beli Breg. This is where the locals had filled up both meanders and had made the river-bad straight, making the water flow away quicker. Thanks to the LIFE Stržen project we will renew, in the Ključi area, 2,1 km of the old water-bed, and 2,5 km in Beli Breg area.

Main goals of the renaturation: 

1. WATER: giving back the Stržen’s river-bed its natural course, enlarge it and by doing so making the water stay in the river-bed for longer periods of time during the dry season
2. ECOSYSTEM PRESERVATION: the renaturation will contribute to higher levels of groundwater and to longer periods of time of water in the water-bed. All this will improve the living conditions for many endangered animal and plant species, e.g. fish, birds and the special bird – the Great Bittern.
3. REINFORCED SELF-CLEANING ABILITY OF WATERCOURSES
4. THE GREAT BITTERN: the renaturation is extremely significant for nesting of this rare bird which needs specific conditions to create a nest in the reeds next to the water flow

 

The renaturation of Ključi area is made financially possible by the LIFE mechanism and also thanks to financial contributions of Slovene Ministry of Environment and Space, some local companies, the Municipality of Cerknica and the Life Stržen Project partners.

THE LOCALS:

The significance of the restoration of Stržen in Ključi was recognized by the owners of the land surrounding the part of the watercourse which will be restored. They have expressed support for project activities. The regulations have been done on private land and have cut many plots of land in half, which prevents some owners access to their own land. They have tried to overcome this obstacle by establishing new roads, culverts, etc.

Redirecting the watercourse will solve this problem. The entire area will be restored and past access points will be re-established. This way, all the landowners will be able to access their property and manage it as a whole.

The total length of the watercourses on Cerknica field was 45 km before the regulations were implemented, but the total length of the straight channels into which the water was redirected is only 33 km. By straightening the riverbeds, the length of the originally meandering streams of Cerknica Lake was reduced by more than a quarter!

Will Stržen’s restoration contribute to higher flooding in the area or have any other negative consequences for the environment?  

Absolutely not! The restoration will contribute to longer water retention time in Stržen’s water-bed in dry season. In times of high water levels the renewed meanders will have no environmental influences at all, except for the already listed positive implications for the lake’s ecosystem.

 

Notranjska Regional Park carried out a pilot restoration of the upper parts of watercourses Goriški Brežiček and Tresenec in 2009. These two watercourses were redirected into their natural meanders with a total length of 1,2 km. These succesfully carried out LIFE projects proved to be the right direction. With the already implemented renaturation of Goriški Brežiček and Tresenec and the on going restoration of Stržen in the area of Ključi and Beli breg, nearly half of the regulated watercourses on Cerknica Lake will be returned into their original riverbeds. Notranjska Regional Park has been actively seeking possibilities of financial support to continue the renaturation of the regulated watercourses on Cerknica Lake, e.g. Žerovniščica and in Lipsenjščica. The key to achieving this goals is good cooperation with local farmers, fishermen and ecologists. Our wish is to return the lake to its image from Valvasor’s time and continue repairing the historical injustice that has been done to it. These violations might not be noticeable to one-time visitors to the lake, but the locals, especially the elderly, can tell you that the lake isn’t what it used to be. We want to preserve the circle of life on our wonderful intermittent lake, created by thousands of animal and plant species.  Last, but not least, humans are also part of it.