[1] The Buynovska reka is considered the main stem of the river[1] and takes its source at an altitude of 1,558 m in the western Rhodope Mountains at 3.4 km southeast of the village of Kozhari, in the immediate vicinity of the border between Bulgaria and Greece.

Downstream of the village of Buynovo, the river turns north and along most of its course flows through deep canyon-like valley until it enters the Upper Thracian Plain at the town of Krichim.

[12] The lower valley of the Vacha is among the prime butterfly areas of Bulgaria, where several species of conservational importance are found, including Zerynthia polyxena, Pieris ergane, Scolitantides orion, Glaucopsyche alexis, Apatura metis, Neptis rivularis, Nymphalis xanthomelas and Melitaea trivia.

Izgoryaloto Gyune nature reserve along its left banks south of Krichim conserves the only population of Greek juniper (Juniperus excelsa) in the Rhodope Mountains, and one of the two in Bulgaria.

Its lower course is included in the River Vacha Thrace protected area under Natura 2000 to conserve hydrophilic communities of tall grasses, alluvial forests of common alder (Alnus glutinosa) and European ash (Fraxinus excelsior) and riparian galleries of white willow (Salix alba) and silver poplar (Populus alba).

[16] Part of the waters of the upper course of the tributaries Devnenska reka and Gashnya are diverted west to the Batak Hydropower Cascade (254 MW).