Amazing colour of that lake, indeed. We fell in love with it from the first time we saw it some 9-10 years ago :D
The water is cold, as small, cold streams from the mountains flow into the lake.

The coastal towns get the water supply form it (Mediterranean coast), and during summers there is less water unfortunately, but depends on year... if during the winter and spring there was enough rain, it is good and we can enjoy in always blue/turquoise colour :)