In the middle of the mountain range of the mountain chain Gailtaler Alpen. Only a few km in the south-east of the Weißensee you can find the Farchtensee in about 985m above sea-level in a parallel valley of the Stockenboier Graben. In the south the basin of the lake is bordered by the Graslitzen, a 2.044 m high summit of the mountain chain Gailtaler Alpen. In the north it is limited by the mountain ridge of the Zlan Nock. The lake is situated in the central part of the mountain chain Gailtaler Alpen, which are formed by lime, dolomite and marl stones out of the Triassic. It is settled in young Quaternary sedimentation.
The shore zone has – with a few exceptions – natural vegetation. In the south forests reach the shore, the north is chiefly formed by wet meadows. In the west and east of the lake you can find earthy lime wet moors, with dense stocks of sedge and little amounts of reed and buck beans. Next to the banks there is a small belt of yellow water lilies.
Hardly populated surroundings. Except of a few houses the environment of the Farchtensee is nearly unpopulated. The Farchtenseestraße is running along the northern shore of the lake, separated from the lake by wet meadows. Only a small creek, coming out of an eastern valley, feeds the lake, but there is a strong runoff with about 140l/s that indicates a bringing in of groundwater out of the surrounding gravel hills. The runoff leaves the lake in the west, goes together with the Tscherniheimer Bach and flows into the Weißenbach, the runoff of the Weißensee.
Lake poor of nutrients. The Farchtensee belongs to the oligotrophic lakes of the Kalkalpen. Regularly high waters bring in dim limes that reduce the temporary visual range strongly. In times without high waters with minor production of algae the visual range can reach 8 m.
Summerlike water temperatures. In spite of being relatively high up, the lake reaches more than 21 °C during midsummer. In early summer the warming up happens rather slowly, the highest temperature is measured between the end of July and the end of August.
Landscape protection area. The Farchtensee and its surroundings of 120 ha were declared Farchtensee landscape protection area (LGBl. Nr. 85/1970).
Red fins are the most dominant species in the Farchtensee. Formerly there were also coarse fish in the lake, but their stock has reduced after the stocking of pike. And there can neither be proved brown trout or lake trout (SCHULZ, 1988), nor capital individuals of pike any more. It could be because of the decreasing food offer (FARKAS).
Highest lying stock of Astacus astacus in Carinthia. The Farchtensee offers the highest situated stock of crayfish in Carinthia. The partly generous vegetation of macrophytes (e.g. large water lily stocks) offers agreeable living space conditions for crayfish. As we know that the population is much larger than the natural area distribution, we must proceed from the assumption that the crayfish have come into the lake by having been set in.