Lake Zurich (German: Zürichsee, Swiss Standard German pronunciation: [ˈtsyːrɪçˌzeː]; Alemannic German: Zürisee) is a lake in Switzerland, that extends southeast of the city of Zurich. Depending on the context, Lake Zurich or Zürichsee may refer to the entire lake or specifically to the section downstream of the Hurden peninsula and Seedamm causeway (between Pfäffikon and Rapperswil). In the latter case, the upstream part of the lake is called Obersee (lit. 'Upper Lake'), while the lower part is sometimes also referred to as the Lower Lake (unterer Zürichsee), respectively.

Lake Zurich is a glacial lake that was formed by the Rhine-Linth glacier. Its main tributary is the River Linth, which rises in the glaciers of the Glarus Alps . The Linth originally flowed directly into Lake Zurich, but was later diverted by the Escher canal (completed in 1811) into Lake Walen (Walensee) from where its waters are now carried to the east end of Lake Zurich (near Schmerikon) via the straightened Linth Canal (completed in 1816).