Batak Reservoir, Mountain reservoir in Rhodope Mountains, Bulgaria.

Batak Reservoir is an artificial lake in the Western Rhodopes, 4 km west of Batak town at 1,108 m altitude. Its main dam is an earthen structure 35 m high with a 273 m crest, faced with loose grey rock and topped by spaced poles; a counter dam in the Kuiloto area is 9.5 m high and 363 m long. The lake covers 21.4–24 km², holds 310 million m³, stretches 17 km at its longest and 4 km at its widest, and contains the 2.2–3.0 ha island of Golaka.

Built between 1954 and 1959, the reservoir is the main leveling facility of the second level of the Batak Hydropower Cascade (254 MW). It collects water discharged from the underground Batak power plant upstream and from derivation channels totaling 128 km, of which 51 km run through tunnels. Its water then flows through a 3 km pressure culvert to the underground Peshtera plant and is used to irrigate 450–500 km² of the Upper Thracian Plain.

The reservoir takes its name from the town of Batak, 4 km to the east. On the western shore stands the mountain resort of Tsigov Chark, while the quieter Danoto holiday area and the small resort of St Constantine lie near the dam in Peshtera Municipality. Anglers fish the lake year-round.

The main approach is the second-class II-37 road from the east; the third-class III-376 branches off just west of Batak and runs along the southern shore to Tsigov Chark, Rakitovo and Velingrad. The dam stands at the northern end of the lake, with the Danoto rest area nearby and the St Constantine resort about a kilometre northeast.

The Batak Reservoir is part of a larger system that includes multiple reservoirs and hidden power plants built underground throughout the mountains. This network of connected water works generates power for the entire region while remaining largely hidden from view.