The Weissensee is a lake in the Austrian state of Carinthia within the Gailtal Alps mountain range. The highest situated Carinthian bathing lake shares its name with the municipality of Weissensee on the northern and southern shore.

The western shore of the glacial lake is located near the Kreuzberg Saddle mountain pass of the Bundesstraße road from Greifenburg to Hermagor. A smaller mountain road runs from the Drava valley via Stockenboi to the eastern end. 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.

Since 1989, in winter the lake is the site of the Dutch Alternatieve Elfstedentocht speed skating competition. Besides skating, ice stock sport and cross-country skiing around the Weissensee is quite popular. A smaller alpine skiing area is situated at the southern shore. In February 2007 the first underwater ice hockey world championship was held at the lake. In January 2011, an Austrian mountain aviator association landed about 30 small aircraft on the frozen surface.

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. Taking a shortcut home, he sledged over a thin patch of ice, fell through and died. His body was never found. In honour of his memory, the spur and a nearby inn were named after him.
Parts of the 1987 James Bond film The Living Daylights were shot at frozen Weissensee.