To the south the ridge of the Eminska Planina forms the boundary with the drainage systems of the Hadzhiyska reka and several small short rivers that empty into the Black Sea.

[2] There are fish populations of Eurasian carp, common chub, Romanian barbel, Flathead grey mullet and others, that support the aquatic birds.

[2] The Dvoynitsa flows in Burgas and Varna Provinces and downstream of Golitsa its valley serves as border between the two administrative divisions.

Its waters in the middle and lower course are utilised for irrigation, the main crops being barley, maize, peaches, apples, grapes, almonds, lavender.

In the 13th and 14th century the Bulgarian Empire constructed the important fortress and town of Kozyak on a height over river banks some 3 km upstream from its mouth, which guarded the only road along the coastline.