I confess the name of Lake Wiestal was new for me. Anyway, as I looked it in the map, I saw with the other 4 lakes you mentioned all of them are in Salzkammergut, close to each other. Basically every austrian regions have some interesting lakes. Gruner See and Erlaufsee are in Steiermark, Klopeinersee in Karnten, Samaranger See in Tirol... I think Tirol is the place where the easiest to find world class diving and skiing as well. But ski is not my piece of cake.

Altough Austria is not a huge country, so we regularly goes there to dive from Hungary, but Tirol is too far away for a weekend trip. So the Samaranger see and Fernsteinsee are still on my "must dive" list in Austria. I think Austria is one of the most interesting destinations in Europe: the Alps, nice lakes, Vienna, Salzburg... There are a lot of nice but cheap B&B accomodations, tidy villages, good diving centers, nice people. I visited many countries, but Austria is still one of my favourites.