THE HISTORY OF THE LAKE LIES IN THE LAKE MUD

After the last glaciation around 15,000 years Before Common Era (BCE), the Würmian glaciers formed a natural dam (end moraine) as they retreated, allowing the emergence of Lake Altaussee from the meltwater. At times, its water level was higher than today and the Altaussee community would have been submerged until prehistory. Later, the water level dropped up to 20 meters below the current level. Lake Altaussee finally rose to its current level when multiple debris flows
blocked the prehistoric outflow.

Im Hochmittelalter, etwa um 800 n. Chr., ereigneten sich im Osten des Sees mehrere große Felsstürze mit insgesamt über 300.000 m³ an Schutt, Geröll und Felsblöcken. Am Seeboden sind daher Steinblöcke mit über 10 m Höhe und 80 m Breite auffindbar.During the High Medieval, around 800 AD, several rockfalls occurred at the east end of the lake, totaling over 300,000 m³ of debris, rocks, and boulders. Boulders over 10 m high and 80 m wide can be found on the lake bottom.

Around 1,100 AD, the Augstbach flowed into Lake Altaussee and was diverted into the Altausseer Traun by human intervention 200 years later.