This lake is an open firth (known also as Vaya lake) of roughly oval shape with maximum length of 9.6 km, maximum width of 4.5 km. and a surface area of 2760 ha. Its depth at places reaches 1.3 m. Thus the Bourgas lake is on the first place rated by size among the natural lakes in Bulgaria. It is separated from the sea by an extensive sand bar where the industrial sector of the town has been built on. Today the Bourgas lake is linked with the sea by a channel ending with a sluice. The rivulets Aitoska, Sandardere and Chukarska flow at the lake’s western part. There are insignificant seasonal and annual fluctuations of the lake’s water level.A rich plant and animal life is a typical feature of the Bourgas lake. It is surrounded by a ring of reed growth which forms in the westernmost part a very large bed. More than 60 species of invertebrate have been found there along with over 20 fish species. So far 254 bird species have been recorded on and around the Vaya. Many of them are rare for Bulgaria or for Europe and 9 of them are among the globally threatened species. Some of the birds like Herons, Cormorants, Black-winged Stilts, Grebes breed there, while other species, mostly Ducks, Geese, Pelicans and Swans spend the winter or roost during migration. This was the main reason to put the lake in the European IBAs List.

An area of 379.4 ha located in the lake’s western part has been designated as a protected site to preserve the breeding colonies of Night Herons, Little Egrets, Squacco Herons and other water birds. Of the wintering species of greater conservation interest are the Pygmy Cormorant – up to 5800 ind.; the Dalmatian Pelican – over 300 ind.; the White-fronted Goose – over 20 000 ind.; the White-headed Duck – over 2000 ind.; the Red-breasted Goose – up to 6450 ind.; the Pochard – over 13 000 ind.; the Shoveler – over 6000 ind.; the Tufted Duck – up to 16 000 ind. Of the breeding birds the Cormorant numbers over 200 pairs, the Night Heron numbers up to 10 breeding pairs, the Little Egret – over 25 breeding pairs, the Squacco Heron – about 10 pairs, the Grey Heron – over 15 breeding pairs, etc.

In the past the Bourgas lake was of the highest bioproductivity in Bulgaria. Annual amounts of fish harvested from Bourgas lake came to hundreds of tons. After the oil refinery ‘Neftochim’ was built the lake’s economic value was almost completely lost. Its ecosystem was especially hard hit during the 1970-ies when no treatment of the refinery effluents was even attempted. However, for several years now pollution of the lake waters has been terminated and it has started gradually to restore its former valuable biodiversity.