The Attersee is close by Salzburg in Austria and is at about 460 m of altitude. The temperature of the water is about 11 – 15 degrees Celsius and the lake is 172 meters deep.

The lake contains 24 spots to dive and you can find them all on this website (see the interactive map in the top right):

http://attersee.salzkammergut.at/detail/article/taucheinstiegstellen.html

See also this movie from Herbert Fleisch, it shows great vis in wintertime:

https://www.youtube.com/watch?v=hakJBxFWwak