Hafnersee

The Hafnersee lies in the Keutschacher Seental, a valley south of Wörthersee in Carinthia. It is one of several small lakes shaped by a branch of the Drau glacier that once cut through the Sattnitz ridge. The lake sits 800 m west of the larger Keutschacher See and rests on layers of ancient rock topped by thick clay and conglomerate deposits. Two streams feed the Hafnersee: the Rodabach from the west and the Penkensee to the south, with groundwater making up a large part of its water supply. The western shore is bordered by wide peat bogs whose humic acids give the water a natural brown tint. Archaeologists found a Neolithic pile-dwelling settlement on the shallow ridge dividing the lake into two basins. The site belongs to the same Moon Lake culture as other lakes in the Salzkammergut and is now protected. In the 1970s heavy nutrient runoff from farms and homes turned the lake green with algae and stripped deeper layers of oxygen. A new sewage system and treatment plant in Klagenfurt reversed the damage by the mid-1980s, restoring clearer water and healthy oxygen levels. Today the lake is classed as weakly mesotrophic, with water temperatures reaching 25 °C in July and ice up to 50 cm thick in winter. Visitors find a narrow, rectangular lake with a shallow sill in the middle separating two deeper basins. The north shore has lawns for sunbathing and a small camping ground, while the south remains largely wild. Beneath the surface live nineteen fish species including pike, zander and the introduced North American largemouth bass. Along the untouched southern edge crayfish patrol the shallows and water plants shelter snails, mussels and aquatic insects. The whole valley, including the lake, forms a 2,532-hectare landscape protection area.