The Dyavolska reka (Bulgarian: Дяволска река, "devil's river") is a 37 km long river in Burgas Province, southeastern Bulgaria.
The river originates under the name Dudenska reka from a spring at an altitude of 440 m, southeast of the summit of Chukara (466 m) in the Bosna Ridge of the Strandzha mountain range. It flows in northeastern direction though a forested valley until the village of Yasna polyana. Downstream of the village it turns east and forms a wide swampy valley until its mouth in a dike-protected riverbed. It flows into the Black Sea at the town of Primorsko. The marshy area at is mouth is known as Dyavolsko blato (Bulgarian: Дяволско блато, "devil's swamp"), covered by common reed ("Phragmites australis"). The swamp is fed by a freshwater spring, has an area of 2.7 km and depth up to 3 m.
