Some 50 kilometres (31 mi) upstream of the station lies the Sihlsee, Switzerland's largest artificial lake, which is impounded by a 33-metre (108 ft) high dam. Studies showed that a failure of this dam could lead to an 8-metre (26 ft) high flood wave reaching the Hauptbahnhof within 2 hours. This threat has led the City of Zürich to develop, publish and test evacuation plans for the affected areas of the city, and especially the station area.[17]