Warm bathing lake. The Hörzendorfer See is situated in a hill country that stretches from the Zollfeld to the west and is formed by the foothills of the Ullrichsberg.The rocky underground essentially consists of the volcanic rocks of the Magdalensberg series, which are covered by quartz-sandstone and quartz conglomerate (Grödener sandstone). The region is formed glacially and covered by mighty moraine sedimentation. During the retreat of the glacier the Hörzendorfer See was filled up by a dead ice substance. The lake basin was sealed by a dam in the east and the lake was dammed up. Originally the lake served as a drainable fishing pond chiefly for fish breeding; nowadays it is a popular bathing lake because of the high water temperature in summer. In winter the frozen lake is visited by numerous sportsmen.
Caused by the strong eutrophication occurrences in 1982 a deepwater diversion was installed, which made the deep waters, which were rich of nutrients and poor of oxygen run into the runoff. The inflow flows into the lake in the west. The runoff leaves the lake in the east, crossing a official pond discharge.
Brooding place for birds. In the south of the lake the natural shore- zone vegetation like reed, "Teichbinse", reed mace and different species of sedges was preserved. The expanding reed belt is the brooding place for the small bittern, great crested grebe, coots and mallards. And this rich offering of fish and small animals attracts a number of migrant birds. In the region of the inflow you can also find a larger amount of reed.
Usage of the surrounding. A large rest-care meadow on the northern shore of the lake is visited by many bathing guests during the months of summer. In the east of the lake there is a road, which is separated from the shore by a narrow reed belt. In the wider surrounding you can see large agricultural areas, where they usually plant corn, as well as several more or less large forest- parcels with mostly spruce or pine- tree monocultures.
Landscape protection area. A main part of the original vegetation around the Hörzendorfer See has been destroyed by human interference and a diverse cultivation- area was built up. The region was declared landscape protection area in 1970, called the Hörzendorfer See- Tanzenberg landscape protection area (LGBl. 36/1970). It has an area of 444 ha.
There are 15 species of fish in the lake:
Pike (Esox lucius)
Bass (Perca fluviatilis)
Lake trout (Salmo trutta f. lacustris)
Catfish (Silurus glanis)
Chub (Leuciscus cephalus)
Bream (Abramis brama)
Carp (Cyprinus carpio)
Bleak (Alburnus alburnus)
Roach (Rutilus rutilus)
Common rudd (Scardinius erythrophthalmus)
Tench (Tinca tinca)
Pike-perch (Sander lucioperca)
Trout bass (Micropterus salmoides)
Sun bass (Lepomis gibbosus)
Crucian carp (Carassius carassius)
Used for angling. Formerly the Hörzendorfer See was managed as a drainable carp pond. Today it is used for angling by the owner. Because of leaky spots the lake had to be layered in autumn 1991 for the stabilization of the drain. For this purpose a major part of the fish was taken out. Up to this time you could also find grass carp and silver carp which had been stocked. During the fishing-out a silver carp of 32, 5 kg was caught.
The main fish of the Hörzendorfer See are carp, pike perch and pike. Out of the Ossiacher See they also stocked bleak. Sun bass came in accidentally together with other stocked species.
In the runoff of the Hörzendorfer See, the Reinitzbach, there are also brown trout, brool trout, gudgeon, rainbow trout and chub.
Population of North-American Signal Crayfish. The Hörzendorfer See lodged a high stock of noble crayfish in former times. But the population has reduced strongly since the middle of the 1980s. With the layering of the lake in the year 1991, because of the stabilization of the drain, the crayfish population has nearly disappeared. After that they set in the American Signal Crayfish. This species of river crayfish can now be found in the Reinitzbach, too. Noble crayfish can neither be documented in the lake nor in the runoff now.