Salzkammergut is a region of many lakes. Most of them are in Upper Austria, a few reach into Salzburg. Most of them are colder than the Carinthian lakes that I’m used to. The climate is harsher here, so if you intend to swim, you’d better come in mid-summer. Mid-August was a safe bet. Still, Traunsee for instance had only 19 degrees Celsius in one of the hottest summers so far.