Lake Altaussee
Lake Altaussee, also known as Altausseersee, is a mountain lake located at the southwestern foot of the Totes Gebirge in the Styrian part of the Salzkammergut. It lies at 712 m above sea level. The center of the municipality of Altaussee is located on the western shore. The Altaussee Traun, which flows into the Danube via the Traun, serves as the outlet of the lake. The largely undeveloped shores and adjacent wetlands of Lake Altaussee provide habitats for numerous animal and plant species and have been under nature conservation since 1959. The Austrian Federal Forests own Lake Altaussee, which is a popular excursion destination due to its beautiful location. Every third year, the lake hosts the Daffodil Festival, Austria's largest flower festival.Geography
The Totes Gebirge surround Lake Altaussee in a horseshoe shape. The Loser lies to the north, with steep flanks that drop sharply to the lakeshore. To the east, the Trisselwand features a rock face that rises approximately 600 meters high. On the northeastern shore, the Seewiese marks the beginning of a trough valley that leads over the Hochklapfsattel to the plateau of the Totes Gebirge. To the south, the Tressenstein follows, while the village of Altaussee in the hilly area of the Aussee Basin is situated to the west. The shores are rocky and steep, particularly in the north, while in other areas, they are partly pebbly, flat and largely undeveloped.
The lake stretches from west-southwest to east-northeast, covering a length of 2.6 km with a maximum width of 1 km, and a surface area of around 2.1 km2. With an average depth of 35 m, the lake basin has steep slopes, except for the northeastern part, where the slope gradually decreases from approximately 40m depth, leading to a relatively large bottom zone with a maximum depth of 53m. The deepest point is a spring funnel near the north bank, which reaches a depth of 73m, while the water volume measures 72.7 million cubic meters.
The lake can be reached via the Altausseerstraße L702. The lake is surrounded by a 7.4 km long circular hiking trail Uferpromenade.Hydrology
The hydrological catchment area of Lake Altaussee encompasses a total area of 54 km2, entirely located within the Totes Gebirge. The lake's primary source of water is from karst springs located at the lake's bottom, which receive underground flow from debris and rock crevices. These springs have an average total discharge of 3750 L/s. Additionally, there are a few small spring outlets along the shores with a combined discharge of approximately 20 L/s. Lake Altaussee demonstrates typical fluctuations in discharge commonly associated with karst springs. In the northeast, there is a small dead ice hole called Lake Osterseen, which is filled by groundwater corresponding to the water level of Lake Altaussee. The Altaussee Traun, the lake's outlet, exits in the southwest at the Seeklause, where a bridge spans the outflow. It carves its path between the rock barrier of the Plattenkogel and the alluvial fan of the Augstbach, which acts as a natural dam for the lake.
Originally, the Augstbach stream flowed into Lake Altaussee 250m north of the lake outlet. However, due to the issue of saline water from the nearby salt mine repeatedly reaching the lake through this stream, the stream bed was artificially relocated before 1530. Since then, the Augstbach has been redirected to flow westward, past Lake Altaussee, and into the Traun River approximately 150m downstream from the lake outlet.
After heavy and prolonged rainfalls, a hydrological karst phenomenon known as "the Liagern" can be witnessed in the Seewiese area. This event occurs due to the presence of two cave entrances situated at different elevations. During this spectacle, vast amounts of water accumulate within a cave in the middle section of the Loserwand. The resulting overpressure causes a large jet of water to shoot out of the cave portal of the Liager hole in a high arc. The process, with some interruptions, only takes about an hour, and the bulk quantities can reach 3000 L/s. The waterfall turns into a torrent in the area of the wall, which tumbles down to the lake and, together with the strong underground inflow, causes the lake level to rise by up to 60 cm within just 12 hours.Geology
Tectonic
Lake Altaussee is a component of the Northern Limestone Alps, which lies on the southwestern edge of the Totengebirge cover, characterized by its abundance of Mesozoic limestones and dolomites from the Triassic and Jurassic periods. Within the western part of the Totes Gebirge, lies the Schönberg group, which is geologically distinct from the Priel group due to a deep incursion furrow. The Wildensee line is a geological structure that stretches from Lake Altaussee, traverses the Hochklapfsattel, extends to Wildensandee Lake, and continues over the Rinnerboden to Offensee Lake. The base of the Loser mountain is composed predominantly of Dachstein limestone, while the Plattenkogel showcases Pedata limestone or dolomite formations, both originating from the Triassic period. The Trisselwand and Tressenstein areas exhibit the presence of Oberalmer Formation and Tressensteinkalk, which formed during the Jurassic period. Scattered around the lake, one can observe remnants of terminal and lateral moraines, offering glimpses into the region's glacial history and the shaping of its surrounding landscape.Former glaciation and formation
During the ice ages, the Altaussee glacier flowed from the Totes Gebirge plateau, flowing over the Aussee basin and reaching the Traun glacier near Bad Goisern. The glacier's movement was instrumental in sculpting the valley's over-deepened basin of Lake Altaussee. About 16,000 years ago, a powerful readvance of the glacier occurred and filled the basin once again, giving it its current form. Simultaneously, as the over-deepened basin was being freed from the ice, a lake began to form at the edge of the ice body. This phase, marked by the presence of a high debris formation around Lake Altaussee's basin, indicates the interaction between the ice body and the lake basin. As the ice eventually disappeared entirely, the alluvial cone adjusted to accommodate the present lake level. Originally, the lake area was likely more extensive, stretching over the Seewiese and reaching the Osterseen. Over the course of the post-glacial period, the lake basin constantly changed its shape as a result of silting up. It is expected that, over tens of thousands of years, the lake basin will eventually vanish once again, further transforming the landscape.Climate
The climate data show a temperature and precipitation distribution typically found in the Northern Limestone Alps: Cool and precipitation-rich summers, with a maximum of 16.2 °C and 220mm in July, respectively, and winters with low precipitation, with a minimum temperature of -2.2 °C in January. Precipitation shows a secondary maximum from December to January. Overall, the annual precipitation was 2041mm with an annual average temperature of 7.1 °C. The Schönberg group, located at the edge of the Totes Gebirge, benefits from frequent cloud accumulation, resulting in above-average precipitation in that area. A comparison with Bad Mitterndorf, situated on the southern side of the Totes Gebirge and approximately 12 km away, highlights the barrier effect of the Totes Gebirge at a similar altitude. Bad Mitterndorf receives annual precipitation of 1222mm at an elevation of 803m above sea level. In terms of snow cover duration, the nearby town of Bad Aussee, located 3 km away, experiences approximately 126 days of winter snow cover.Limnology
Circulation
Lake Altaussee is classified as a dimictic lake. In spring after the ice melts, the water body mixes and brings oxygen-rich water into the depths. In the summer half-year, a distinct thermocline forms, and only the surface layer warms up, in autumn mixing occurs again, followed by ice formation. Strict stratification conditions are present in Lake Altaussee. The epilimnion has only a very small thickness of about two meters. The metalimnion lies at a depth of about five meters. The uniformly temperate hypolimnion begins at 10 meters. The strikingly high position of the metalimnion is due to the relatively wind-protected location and only moderate flooding of the lake. After the spring circulation, surface water temperatures gradually increase, reaching a long-term average of 16.3 °C in August. However, between 2000 and 2006, the mean August temperature was higher at 18.4 °C, nearly 2 °C above the long-term average. The highest recorded water temperature in the lake was 21.8 °C during the summer of 2003. At depths below 15 meters, temperatures average around 4.6 °C. Throughout the summer stagnation phase, the hypolimnion warms up by an average of only 0.3 °C. The lake is typically covered by ice for an average of 57 days each year.Trophy
The lake has a low concentration of nutrients and is thus oligotrophic. Measurements in the years 2000 to 2006 showed an average phosphorus content of 6.7 μg/L. Due to the discharge of untreated wastewater, a eutrophication trend could be detected in the years 1963 to 1973 and the oxygen saturation above ground was already decreasing. In addition, bacteriological tests revealed the presence of salmonella. As a result, remediation measures began, which were completed in 1980 with the construction of a regional association sewage treatment plant with a third treatment stage in the municipal area of Bad Aussee. The hygienic situation of the bathing areas improved rapidly and the oligotrophic condition of the lake could be maintained. Several supply and disposal pipes run through the lake, connecting the rest areas at the Seewiese and the beach café located on the southern shore to the sewage system. Due to the low phytoplankton concentration and low algae growth, the average summer visibility depth is 8.9 meters.