Ossiacher See

General Description

With its 10, 79 km² the Ossiacher See is the 3rd largest lake of Carinthia. At all times it was a popular destination for excursions and holidays. The natural surrounding and the pleasant water temperatures up to 27 °C attract bathing guests to stay on its shores with their 9 bathing beaches.

Embedded between woody hills. The name Ossiach can be derived from the Slavic “osoje”, which means “shady side”. The lake is situated between the woody steep slopes of the Gerlitzen in the north and the western foothills of the Ossiacher Tauern in the south. The lake basin is lowered in old crystalline rock bulks, which partly are covered by glacial gravel. Two basins that are parted from each other by a dam down in a depth of 10 m, characterize the lake. The eastern, smaller basin (3, 9 km²) is 11 m deep, the western, large basin (6, 9 km²) is deeper than 52 m. Because large areas of the lake are rather flat its average depth is 19, 6 m, which is not much compared to its area.Sanierungsprojekt Bleistätter Moor.

Stabilization Project Bleistätter Moor. The Tiebel with 1.750l/s and several smaller brooks out of the Gerlitzen region feed the lake. Tributaries out of the south are unimportant. In the east of the lake there is the Bleistätter Moor with about an area of 6 km², which is flown through by the Tiebel. In the 1930s the moor was drained and since then is intensively used agriculturally. Pump stations transport the drain waters which are rich in nutrients into the Tiebel and further on into the Ossiacher See. Within the Restoration Project Bleistätter Moor parts of the POLDER area shall be re-structured and flooded. The purpose of these measurements is the reduction of floating stuff and nutrients in the lake.
The runoff of the lake, the Ossiacher Seebach, has a water volume between 2.610l/s (1986) and 5.890 l/s (1965). The annual average volume is 3.320 l/s.

Bathing water quality – limnologically unobjectionable. Limnologically the Ossiacher See belongs to the weakly MESOTROPH lakes, which are less burdened with nutrients and therefore of a superior bathing water quality. The lake is holomictic, meaning it is mixed through down to the ground during the circulation phases in spring and in late autumn. During the summer months the surface water warms up to more than 24 °C. The water substance is strongly piled up from May to November. The surface layer, the epilimnion, reaches a depth of about 6 m. Deeper it is quickly getting colder and in a depth of 15 m it reaches only 4 °C to 5 °C. The ice sheet only lasts for a few weeks, in mild winters there is not any at all. The limnological development of the Ossiacher See is already observed since 1931.

Natural left lake and shore areas of the lake are declared nature- and landscape protection area. Seven landscape protection areas together have about 370 ha:
NSG Tiebelmündung: 30,5 ha, LGBl.30/59,19/ 60, 16/ 68;
NSG Jammernspitz: 5,1 ha, LGBl. 31/ 59, 19/ 60;
NSG Meerspitz: 8 ha, LGBl. 65/ 57;
NSG Ossiacher See – Westbucht: 8 ha, LGBl. 15/64;
LSG Ossiacher See – Ost: 284 ha, LGBl. 26/70;
LSG Ossiacher See –Westbucht: 20 ha, LGBl. 37/ 70;
LSG Bodensdorf: 10 ha, LGBl. 25/79.

Tourism

A popular holiday destination. The Ossiacher See was already visited by “ Sommerfrischlern” in the first half of the 19th century. Today many hotels and gastronomic institutions in the neighboring villages offer the guests numerous possibilities of recreation and activities. The Convent Ossiach on the southern shore is well known not only because of the Benedictian monastery out of 1024 but most of all because of the events of the Carinthian Summer.
In the region around the lake a busy tourism has developed. Over–night- stays have risen from 100.000 at the beginning of the 1950s up to about 2 million. Annenheim, Sattendorf, Bodensdorf, Steindorf and Ossiach are the most important holiday resorts directly situated at the lake. The largest town in the catchment area is Feldkirchen with about 7.800 inhabitants.

Around the lake by bike. You can go round the lake by bike. The excursion passes the spawn protection area at the west end of the lake, near the Ossiacher Seebach (runoff). This is a wet area of 6, 6 ha which offers food and protection to fish, plants, water- and songbirds because of its rich structures. Near Feldkirchen in the east of the lake there is even a small airport (ICAO- LOKF; Tel.: +43 (0) 4276 27 07) for sailing planes. Two liners run on the lake from the beginning of May until the end of October and stop at 9 destinations.
Stift Ossiach  
Burg Landskron Adler- Arena
Affenberg: www.affenberg.com *Kanzelbahn auf die Gerllitzen: www.gerlitzen.com

Fish Stock

During an investigation in the years from 1994 to 1997 (FARKAS & OLSACHER, 1998) 21 species of fish were documented:

Pike (Esox lucius)
Eel (Anguilla anguilla)
White fish (Coregonus lavaretus) White trout
Lake trout (Salmo trutta f. lacustris)
Catfish (Silurus glanis)
Chub (Leuciscus cephalus)
Bream (Abramis brama)
White bream (Abramis björkna)
Carp (Cyprinus carpio)
Bleak (Alburnus alburnus)
Roach (Rutilus rutilus)
Common rudd (Scardinius erythrophthalmus)
Tench (Tinca tinca)
Pike-perch (Sander lucioperca)
Sun bass (Lepomis gibbosus)
Vimba vimba (Vimba vimba)
Crucian carp (Carassius carassius)
Rainbow trout (Oncorhynchus mykiss)
Burbot (Lota lota)
Barbel (Barbus barbus)

Decrease of variety in fish species. Findenegg`s species cannot be documented any more. Either its population is so small or has disappeared. The decrease of bitterling might have taken place together with the decimation of the GROSS mussels. The originally very large population of catfish was strongly decimated probably because of the eutrophication. In former times extremely large catfish were caught, e. g .one in 1946 with 65 kg and a length of 230 cm. FINDENEGG (1934) mentions the ide in the lake. He appeals to the biologist HAEMPEL. More probably it refers to the chub.

The main fish in the lake is the bream, which makes up to 30 % of the fish population. In the course of an electric fishing of bream during spawn time they caught about 10 t a day. The roach population could be out- dated, you can only find large individuals, while young ones are seldom. The caught heads of pike are strongly decreasing, too, which can be caused by the going back of macrophytes. By this the pike misses suitable spawn conditions and food fish in this region.

A stocking of white fish in the 19th century did not bring any success, so they tried it again in 1982. After some time an own population has developed.
Now the white trout with 10 % has the 3rd position in the lake behind bream and roach. The population of trout is rather small because of the relatively high summer temperatures and the lack of suitable spawn places.

Every year they stock carp for sports fishing, because there is no natural reproduction any more. The population of bleak has gone back, too. In former times they were a remarkable food offer to the catfish. HARTMANN (1898) tells that at spawn season bleak were caught en masse and eaten as ingredients to potatoes, STERZ and POLENTA in winter. The reason for their decrease might be the dragged in WANDERMUSCHEL (Dreissena polymorpha), which resulted in the fact that bleak avoided their habitual spawn places (FARKAS & OLSACHER, 1998). In spite of that, the annual profits in the Ossiacher See even are about 20 kg/ ha.

Flat water biotope as a spawn region. At the beginning of 2000 they built a flat water biotope of about 5 ha at the runoff. First tests have shown that it is perfect as a spawn- and living place for roach, red fin, bass, pike and catfish. After flooding in spring they observed large quantities of bleak and pike there. So this flat water surface has positive results on the entire fish population of the Ossiacher See.

Angling. The lake is parted into 30 fishing plots.

Fishing Permits

Fishery Association Äsche: phone: +43 (0) 4242 56368-22
Falle Fischertreff: phone: +43 (0) 4242 32540-44
Kärntner Jagdstuben: phone: +43 (0) 4242 28826
Carinthian Fishery Association: web: www.kaernten-fischerei.at

Occurence of Crayfish

Sport divers have seen superior crayfish in the lake again and again. Probably they have come through smaller tributaries out of some pond of the Ossiacher Tauern, where they often can be found. During the last years they were also seen in the upper Seebach, the runoff of the lake. In the Ossiacher See in 1880 the crayfish plague evidently appeared for the first time (HAWLITSCHEK, 1892). Up to this event at the end of the 19th century nearly all Carinthian lakes were populated by a dense stock of Astacus astacus. This plague caused by a SCHLAUCHPILZ (Aphanomyces astaci) has cropped up in Carinthia at the end of the 19th century in several waves and has done an immense damage. These waves but also the stocking of eel, a not native species, have prevented a denser population of crayfish in most of the larger lakes in Carinthia.

Remedial Actions

Catchment Area

Valuation of the ecological status. The catchment area of the lake is the region, out of which the surface- and the underground waters flow into the lake. The borders of this area are formed by the watershed. The cartographic description of these catchment areas referring to the usage is the base for the valuation of the ecological status in regard to the general water instructions (WFD). All the fundamental data are registered in a data bank. With the help of the software Arc View GIS, version 3.2, the analysis of the geographic information took place. The topographic state, the natural vegetation and the antrophogen usage of the catchment area deliver important information about nutrient- and pollutant burdens.

Vegetation

There are 40 different forms of vegetation. The descriptions are out of HARTL, STERN and SEGER, 2001, “The Map of Carinthia`s Current Vegetation”. The geo-referenced data out of this work were blended with the catchment area and transferred into the data bank.

They differentiate 40 forms of vegetation. To have a better view on the results they are comprehended in the following tabulation in these main groups: intensively used agricultural areas, farming green-land, forests, surface-waters, built up areas, Alps and others.

Utilization

Utilization

34 forms of utilization in the catchment area. They were geo-referenced and blended with the digital register (DKM) out of 2003.The granted data were transmitted into a data bank and now afford information about the dimensional distribution of the different forms of utilization. The 34 forms of utilization have also been comprehended in the main groups like it has been done for the vegetation groups.