|Primary inflows||Tiebel Creek|
|Primary outflows||Seebach to Drava river|
|Max. length||11 km|
|Max. width||1,700 m|
|Surface area||10.5 km²|
|Average depth||19.6 m (64 ft)|
|Max. depth||52 m (171 ft)|
|Water volume||206 km³|
|Residence time||1.8 years|
|Surface elevation||501 m (1644 ft)|
|Settlements||Annenheim, Sattendorf, Bodensdorf, Steindorf, Ossiach|
It is situated in the southern Nock Mountains range of the Gurktal Alps along the road between Villach and Feldkirchen, at a height of 501 m (1,644 ft). It reaches a maximum depth of 52 m (171 ft), the surface area is about 10.5 km2 (4.1 sq mi).
Lake Ossiach is a dimictic lake with mixing periods in spring and in late autumn. In summer the waters reach 28°C. Several uninhabited parts of the shore are protected as natural reserves.
There are five main villages surrounding the lake, all of them mainly dependent on summer tourism: Annenheim and Sattendorf, parts of the Treffen municipality, Bodensdorf and Steindorf, all located on the northern shore, and Ossiach with Ossiach Abbey, after which the lake is named.