Lake Zurich. Lake Zurich is a lake in Switzerland, that extends southeast of the city of Zurich. Depending on the context, Lake Zurich or Z??richsee may refer to the entire lake or specifically to the section downstream of the Hurden peninsula and Seedamm causeway. In the latter case, the upstream part of the lake is called Obersee, while the lower part is sometimes also referred to as the Lower Lake, respectively.