Almsee is a lake in Upper Austria's part of the Salzkammergut in the Almtal valley, 11 kilometers (6.8 mi) south of the village of Grünau im Almtal. The lake lies in the northern portion of the Totes Gebirge mountains and is about 2.3 kilometers (1.4 mi) by 700 meters (2,300 ft) wide.
The lake drains through the Alm river. Since 1965, the area around the Almsee is under nature conservation. Konrad Lorenz made important observations of the Greylag Goose at the lake.