Lake Klopein (German: Klopeiner See, Slovene: Klopinjsko jezero) is a lake near Völkermarkt in Sankt Kanzian in Carinthia, Austria.
Lake Klopein is the remaining lake of the previously larger lake area, which has spanned over today's Kühnsdorf area.
Lake Klopein is primarily a still lake. Only a few little streams are flowing into it. The result is a very high water temperature, reaching up to 29°C.