Lake Durankulak (Bulgarian: Дуранкулашко езеро) is a brackish lagoon (liman) in northeastern Bulgaria, separated from the Black Sea by sand dunes and a beach strip.

[1][2] It is situated along the Bulgarian Black Sea Coast near the village of Durankulak in Dobrich Province, some six kilometers south of the Bulgaria–Romania border.

It is a protected area with many rare plant and animal species and also contains the archaeological site of Durankulak, situated on the larger of the lake's two islands.

It was formed about 10,000 years ago as a result of the sinking of land masses due to epeirogenic movements of the Earth's crust and the intrusion of seawater into the nearby mouths of rivers flowing into the Black Sea.

It has two main arms, the smaller northwestern begins at the bridge of the first class I-9 road at Durankulak and the southwestern one is fed by the river Shablenska reka.

Due to the irregular river flow and the low rainfall, the lake is mainly fed by karst springs — about 80% of the total water volume.

[8] Over 80% of the vegetation-covered area is occupied by common reed (Phragmites australis) communities, followed by narrowleaf cattail (Typha angustifolia), broadleaf cattail (Typha latifolia), triangular club-rush (Schoenoplectus triqueter) and common club-rush (Schoenoplectus lacustris).

Other rare nesting species included in the Red Book of Bulgaria are red-footed falcon,[25] black-winged stilt,[26] pied avocet,[27] little tern,[28] Eurasian bittern,[29] purple heron,[30] red-necked grebe,[31] garganey,[32] spotted crake,[33] little crake,[34] bearded reedling,[35] river warbler,[36] Eurasian penduline tit,[37] calandra lark,[38] black-winged pratincole, etc.

[23] The lake hosts freshwater fish fauna of 23 species,[47] including the only proven population of wild Eurasian carp in the country,[48] as well as rare species, such as Pontic shad,[10] Black Sea shad,[10] Ukrainian stickleback,[49] Black Sea sprat,[50] crucian carp,[51] Danube bleak, etc.