Grüner See (Green Lake) is a lake in Styria, Austria in a village named Tragöß. The lake is surrounded by the Hochschwab Mountains and forests. The name "Green Lake" originated because of its emerald-green water. The clean and clear water comes from the snowmelt from the Karst mountains and has a temperature of 6–7 °C (43–45 °F). During winter, the lake is only 1–2 m (3–7 ft) deep and the surrounding area is used as a county park.
However, in spring, when the temperature rises and snow melts, the basin of land below the mountains fills with water. The lake reaches its maximum depth of around 12 m (39 ft) from mid-May to June and is claimed to look the most beautiful at this time. In July, the water begins to recede.