Hallstätter See or Lake Hallstatt is a lake in the Salzkammergut, Austria, located at 47°34′43″N 13°39′38″E. It is named after Hallstatt, a small market town in Austria, famous for its salt mining since prehistoric times and the starting point of the world’s oldest and still working industrial pipeline – for brine to Bad Ischl (since 1596) and further to Ebensee.
Since about 1970/1980 the only ship-mail-line of Austria crossed the lake from the railway on the east shore to the town in the west. In winters the road on the west shore tended to be blocked by high snow or the risk of avalanches. When the ice on the lake was thick enough, a sled pulled by men or horses, later a motorized track vehicle was used to transport mail and persons.
Later a tunneled road was built through Hallstatt and the mail switched to transport by bus and truck.
Its surface is approximately 8.55 km2 (3.30 sq mi) and its maximum depth is 125 metres. It is a popular destination for tourists, especially scuba divers.
The fixed exit weir, a 500 years old protected monument, has no bypass und therefore once caused high waters into some houses of the town of Hallstatt on 18, June 2013.