Attersee (less commonly also Kammersee, English sometimes Lake Atter) is a lake in the Upper Austrian part of the Salzkammergut, in the district of Vöcklabruck, and lies at an elevation of . The outflow from Attersee passes through a weir into the Ager river, which flows via the Traun river into the Danube. This nutrient-poor lake, with its varied shorelines, provides habitats for many animal and plant species and has been designated a Natura 2000 site since 2006. With a water surface area of over , it is the largest lake situated entirely within Austria. At , it is the second-deepest lake in Austria after neighbouring Traunsee, and with a water volume of almost , it is surpassed only by (the entire) Lake Constance. The Attersee is owned by the Austrian Federal Forests, is a major tourist destination in Upper Austria and a popular swimming lake, as well as a diving and sailing area. On the shores of the Attersee lie the remains of pile-dwelling settlements from the Neolithic, which form part of the UNESCO administered World Heritage Site known as "Prehistoric pile dwellings around the Alps".
Geography
Attersee is situated in the Upper Austrian Salzkammergut region, in the district of Vöcklabruck. The larger towns on its shores are Seewalchen and Schörfling to the north, Weyregg and Steinbach to the east, and Unterach, Nußdorf and Attersee to the west. In addition to these municipalities, the municipality of Berg im Attergau also shares part of the lake’s surface area.
The lake, which stretches from north to south, is long and has a maximum width of . Its surface area is approximately , and its average depth is . The deepest point is given as in the official Austrian map. In 2014, divers reported discovering a point with a depth of . The volume of water is .
Shore
The Attersee has a shoreline of . The entire shoreline is heavily built-up, and the majority of it is privately owned and not open to the public. Many towns and villages on the Attersee have their town centres on the shore or close to it. There are church towns such as Weyregg am Attersee, as well as planned church towns such as Unterach and Steinbach. Scattered between the settlement centres are individual farms, small settlements and communities with residential and holiday homes. The lakeside areas were heavily developed in the 1970s and 1980s. Shops, restaurants, residential buildings and second homes line the shores. This has resulted in the shoreline being built up with jetties, boathouses, boat ramps, steps, walls, blockwork or rock fill. In those sections of the shoreline that are too steep for development, roads usually run alongside reinforced embankments that have replaced the natural shoreline. Around 87 per cent of the Attersee shoreline is significantly impaired. Particularly affected are the eastern shore, the northern shore and the northern part of the western shore, as well as the section between Misling and Unterach. Only 13 per cent can still be classified as near-natural or natural. The longest continuous natural sections are located between Dexelbach and Parschallen, between Aufham and Dickau, near Schwend and in Burgbachau.
Morphology
On the southern shore lie the foothills of the Schafberg, whilst on the south-eastern shore, as far as Steinbach am Attersee, lies the western end of the Höllengebirge. The mountains there reach heights of between and drop steeply down to the lake. Most of the eastern shore, as well as the entire western shore, is framed by wooded, gently sloping mountains and hills, which taper off at the northern edge.
The lake basin is divided into three sub-basins: a southern basin, a central basin and a northern basin. The deepest point in the southern basin, at 169 m, is situated approximately north of Weißenbach am Attersee. It extends as far as the line between Stockwinkel and Seefeld. The central basin, which is up to deep, extends as far as the line between Nußdorf am Attersee and Alexenau. The underwater morphology is determined by the surrounding rock formations. Here and there, one finds buttes that have not been completely eroded. There are three prominent elevations in the central basin: an underwater mountain rising to a depth of around , the A. Müller Peak and the Laichberg. The latter lies in the centre of the lake near the village of Nußdorf, in the middle of a basin deep, and rises to below the water’s surface. The shores on the eastern side are considerably steeper than those on the western side, as the Höllengebirge mountain range extends its rock faces underwater, as is the case at the Schwarze Brücke (trans. Black Bridge) near Seeleiten. The northern basin, which is up to deep, is predominantly characterised by gently sloping shores. Litzlberg Bay is separated from the rest of the lake by a large embankment. On this embankment lies a small island on which stands Litzlberg Castle.
Transit The area can be reached via the West Autobahn (A1) with the Seewalchen and Sankt Georgen junctions. Two trunk roads run alongside the lake: the Attersee Road (B151) on the western shore and the Seeleiten Road (B152) on the eastern shore.
The lake is nowadays accessible via two branch lines. The Kammerer, a standard-gauge railway, completed in 1882, branches off from the Western Railway at Oberthalheim and runs to Kammer am Attersee at the northern end of the lake, to the right of the river Ager. The line is electrified at 15 kV, 16.7 Hz, it is owned by Austrian Federal Railways (ÖBB Infra) and operated by (ÖBB Passenger Services). Some of the Cityjet trains used on this route also run through to Attnang-Puchheim via Vöcklabruck from Kammer.
The Atterseebahn, a metre-gauge railway, opened in 1913, connects the town of Attersee on the western shore with Vöcklamarkt, which is also on the Western Railway. The line is majority-owned by Stern Gruppe and is electrified using 750 V direct current. At Vöcklamarkt station, passengers can change to trains on the Western Railway directly from the same platform.
The Unterach–See local railway linked the ferry terminals at Unterach on Attersee and See on Mondsee lake from 1907 to 1949. It was operated by Stern & Hafferl as a metre-gauge tramway electrified with 550 V DC.
Up until 1914, several railway lines were planned along the Attersee. However, these were never built due to the First World War and the resulting shortage of materials. The planned routes had already been commissioned and surveyed. The plans included a standard-gauge line that was to branch off from the Western Railway at Frankenmarkt and run via Sankt Georgen, Attersee, Seewalchen, Kammer, Weyregg and Weißenbach to Bad Ischl, where it would connect with the Salzkammergut railway line. This line would have utilised part of the Atterseebahn track bed, which would have been converted to standard-gauge for this purpose between Sankt Georgen and Attersee am Attersee. Also planned was a standard-gauge line which, coming from Straßwalchen, was to branch off from the Western Railway at Rabenschwand and run via Zell am Moos, Mondsee, Innerschwand and Unterach to connect with the aforementioned line at Weißenbach. To relieve pressure on the Western Railway, a railway line was also planned from Weyregg via Kammer to Gmunden, which was to connect north of Gmunden to the Salzkammergut Railway. The route roughly corresponded to the course of the later Western Highway between Schörfling and Regau. A parliamentary resolution for this line had already been passed in 1913.
Hydrology
The hydrological catchment area of Attersee covers a total area of . Attersee forms the final link in a chain of lakes that begins with Fuschlsee lake in the south-west and Irrsee lake (Zeller See) in the north-west. The water from both lakes flows into Mondsee lake and from there, via the Seeache in the south-west near Unterach, into Attersee. The Seeache accounts for 58 per cent of the total inflow. In addition, there are a number of other tributaries, such as the Weyregger Bach, the Alexenauer Bach, the Kienbach, the Äußerer Weißenbach, the Loidlbach, the Burggrabenbach, the Parschalenbach, the Dexelbach, the Nösstalbach and the Ackerlingbach, as well as numerous smaller surface and underground tributaries. The lake drains into the Ager at its northern end, between the municipality of Seewalchen and Schörfling. The water renewal period is 7 years, which is the highest theoretical water exchange rate of any lake in Upper Austria. The average water temperature is . The minimum water temperature, as measured near the surface between 2007 and 2010, was , whilst the maximum was .
The water level is regulated by a weir at the lake’s outlet. As a result of this artificial intervention, the average water level is around higher and the natural annual fluctuation in water level is dampened. Nevertheless, there are regularly severe spring floods. Whilst maximum average water levels used to be reached from around April to May, they now occur about a month earlier (March to April). The lowest water levels are reached, now as in the past, primarily in autumn (October to November). According to records, between 1897 and 1913, the Attersee, with an average water level of , exhibited maximum water level fluctuations of and average annual fluctuations of . The range of the monthly averages was . For the period from 1976 to 2000, the corresponding figures were , , and .
Geology Tectonics
Attersee lies within the area of three major tectonic units. To the south lie the Northern Limestone Alps, followed by the Flysch zone comprising the Rhenodanubian flysch, which is intermittently interrupted by the Ultrahelvetian. The Northern Limestone Alps consist of the Staufen–Höllengebirge nappe (Tirolikum), in front of which lies a narrow strip of the Langbath Zone (Bajuvarikum). This area forms the southern shore and extends along the eastern shore roughly as far as the village of Forstamt. The majority of the Attersee region is occupied by the Rhenodanubian flysch. In a narrow strip between Nußdorf am Attersee in the west and Alexenau in the east, the Ultrahelvetian formation is exposed.
Past glaciation and formation Like all the lakes in the Salzkammergut, the Attersee is also the result of the activity of glaciers during the . During the Ice Ages, the Traun Glacier flowed from the Hoher Dachstein and Totes Gebirge plateaus via lateral branches through the Isch Valley and the Weißenbach Valley into the Attersee region. In doing so, the glacier carved out the deep-cut tongue basin of the Attersee. The ice advance during the Mindel glaciation was the most powerful, and the ice flow from the Attersee trough flooded all the neighbouring valleys in the flysch zone, forming a widely extending foreland glacier from which the Buchberg near Attersee just about protruded as a nunatak. The subsequent ice ages gave the lake basin its present extent and shape. During the Late Glacial period, residual ice in the south and the moraine wall in the north blocked the outflow, resulting in the formation of a lake with a water level of approximately . The slow incision of the Ager river into the terminal moraine lowered the lake level to its present height. Following the final retreat of the ice and the formation of Attersee, extensive deltaic deposits accumulated at all the major tributaries. The delta sediments of the Äüßerer Weißenbach fill the entire Weißenbach valley to a thickness of around . However, extensive delta formations have also developed at the mouths of the streams on the eastern side of Attersee due to the high volume of debris. Compared with the other large lakes in the Salzkammergut, silting of the Attersee basin is occurring more slowly, as the Mondsee, the Fuschlsee and the Irrsee lake (Zeller See) act as sediment catchers and silt traps upstream of it. The lake basin will have disappeared again in around 500,000 years.
Mass movements