State natural reserve "Lousy lake, located 3 km South-East of the village Demin (shpakovskiy district, on the borders of the river basins yegorlyk and Grachevka, is a natural endorheic lake in the Stavropol upland. Reserve, a total area of about 259, 45 hectares, is situated at altitude 505 m above sea level. The lake is very ancient, it is more than a million years.

Famous scientist-ethnographer V. G. Gnilovskaya associates the name of the lake with an abundance of insects that live near the water surface - water fleas, water striders, Cyclops and others. Under the statement of the Russian scientist, social activist and local historian Gregory Prozriteleva, originally it was called Use that is translated from Tatar as "three". So the Tatars called found near the cross that was erected by ancient Christians.

The researchers who conducted surveillance of the lake in recent years, noted that in the 50-ies of XX century it is almost completely dry up in the summer and turned into a muddy reeds of the swamp. In 1995, after heavy rains the water level in the lake is rather rose. Fluctuation of water volume in the lake has resulted in a change of its natural fauna.

The reserve is inhabited by such birds as the water hen, Heron, snipe-black-winged stilt and the coot. In the reeds usual marsh Harrier. There are also marsh frogs, turtles, leeches and water snakes. On the flights there are always swans stop. Fish in the lake are carp, carp and carp. In the bottom sediments of the lake is a Lousy burial spores and pollen of plants that grow adjacent to the lake territories during Holocene and Pleistocene.

Only on the territory of the reserve "Lousy lake there are 25 species of meadow-marsh plants, among which are 8 species of sedges (false-sulfur, early, coast, pigweed, economedia, hairy, blunt and chernogoloka).