Terkos Basin This is an IBA in Danger! 

Country/territory: Turkey

IBA criteria met: A1, B2 (2004)
For more information about IBA criteria, please click here

Area: 160,351 ha

Doga Dernegi
IBA conservation status
Year of assessment (most recent) Threat (pressure) Condition (state) Action (response)
2016 very high unfavourable medium
For more information about IBA monitoring, please click here

Site summary
The Terkos Basin, which includes the Terkos Lake, is one of Istanbul's oldest water resources. The Basin is located to the north of Çatalca Peninsula which is mostly within the boundaries of the province of İstanbul. The KBA continues north within the boundaries of the Kırklareli province, until the Kıyıköy coasts. The Basin is surrounded by the Istranca Mountains to the west and the Terkos Lake to the east. 

The KBA contains a rich flora with its forests, heathland, freshwater and sand dune ecosystems. The KBA has a dominant forest flora and is also home to the largest swamp forest in Turkey. Heathland can be found in the dry parts of the forests and on the southem slopes. Being unpolluted, the lake has a well preserved natural life in the basin with a rich wetland ecosystem containing rare plant species. The Danamandıra Lakes, located in the middle of the KBA, includes heathland and swamp forests together with a rare acidic wetland.

There are 17 plant taxa living in KBA. Some of them are breeding waterfowls such as: Ferruginous duck (Aythya nyroca), Lesser spotted eagle (Aquila pomarina), Little bittern (Ixobrychus minutus), and Squacco heron (Ardeola ralloides) are some of them. Most of them are endangered: Red breasted goose (Branta ruficollis), White-tailed eagle (Haliaeetus albicilla) and Greater spotted eagle (Aquila clanga). The lake hosts more than ten thousands birds in the same time in winter.

Leading important mammal species in KBA are Long-fingered bat (Myotis capaccinii), Mediterranean horseshoe bat (Rhinolophus euryale), Lesser mole rat (Nannospalax leucodon), and European ground squirrel (Spermophilus citellus). There is also Eurasian otter (lutra lutra) around Motor Deresi. Terkos lake is also important for amphibians such as: European fire-bellied toad (Bombina bombina) and southern crested newt (Triturus karelinii). KBA is also important for a kind of damselfly, Somatochlora borisii which is narrow expanded.

Since the end of the nineteenth century, Terkos Lake has been utilised as one of İstanbul's most important drinking water reservoirs, and accordingly this has afforded some protection to the lake and surrounding habitats. Early manipulation of the water level of the lake (including raising the level and digging a new cut to the sea) have apparently little affected the vegetation and flora. However during the mid 1990s the Istranca Water Supply Scheme has supplemented the quantity of water from the lake's natural catchment with that of water from a series of rivers to the west. As of 2000, six out of seven proposed dams have been completed on streams as far west as Kıyıköy (Midye), with proposals to intercept further streams as far west as Demirköy (close to the Turkish-Bulgarian border). The effect of altered water levels (they have apparently been significantly raised), and changes in water chemistry on the vegetation and flora is not yet known. However, anecdotal evidence suggests that the water clarity in 1998 was reduced compared with that of 1994, and that populations of Stratiotes aloides had declined dramatically. Monitoring of this situation is essential.

Afforestation of the sand dunes at Terkos has been undertaken to control erosion in the sand dune zone, deemed to represent a considerable threatto the water resources of the adjacent Terkos Gölü. 

Demand for high quality housing in rural areas poses another growing threat. One major development (the Durusu Park development at Deliyunus, started in the mid 1990s) will cause severe damage to one of the largest remaining complexes of limestone grassland within the site, and may set a precedent for further development close to the edge of Terkos Gölü. Extensive gravel extraction in the Sinekli area is destroying substantial areas of heathland and coppice on the gravel capped hills in the area. The site is listed as one of IBAs in Danger in Turkey in 2015 and 2016.

Recommended citation
BirdLife International (2023) Important Bird Area factsheet: Terkos Basin. Downloaded from on 08/06/2023.