The Weissensee (German spelling: Weißensee) is a lake in the Austrian state of Carinthia within the Gailtal Alps mountain range.

The western shore of the glacial lake is located near the Kreuzberg Saddle mountain pass of the Bundesstraße road from Greifenburg to Hermagor.

Despite its elevation of 930 mAA (3051 ft), the lake surface can reach 24 degrees Celsius in the summer months, while in winter the water freezes over completely and allows skaters to move freely on the ice.

Along the shore are banks of chalk originating from the surrounding mountains of the Southern Limestone Alps, which give the waters its characteristic colour and the Weissensee ("White Lake") its name.

A prominent mountain spur at the northern shore, Ronacherfels, is named after a local peasant who died in the winter of 1916 while steering a sleigh on the frozen lake.