This is the Green Lake, situated in Tragoess, Styria, Austria. The lake sits at the foot of the snow capped Hochschwab mountains.
The lake looks unusual, in that it looks like an underwater park. That is because it is!
In the wintertime, the lake is almost nonexistent and the area is used as a park, which is a favourite among hikers.
In the springtime however, the ice and snow on the mountains melts, and this melt-water fills the basin below. The park is filled with this ice cold, almost crystal clear water. The lake looks green in colour due to the foliage beneath.
The water levels rise from about one or two metres deep in the winter to as much as 10 metres in the late spring and early summer.
The waters are at their highest in June when it becomes a mecca for divers keen to explore the rare phenomenon, before the waters recede at the end of July.
For more photos and a video see here: http://www.myamazingearth.com/2012/08/austrias-green-lake-amazing-and-beautiful-flooded-meadow/