[1] The river takes its source under the name Chakarlia an altitude of 502 m in the Dervent Heights, some 7005 m south of their highest point Gyurgenbair (555 m), which is situated in Bulgarian territory just north of the Bulgaria–Turkey border.

It flows in a narrow forested valley through the northern slopes of the Dervent Heights in direction northwest.

It flows into the Arapliyska at an altitude of 117 m some 200 m east of the village of Chernozem.

[1] Its drainage basin covers a territory of 159 km2 or 45.3% of the Popovska reka's total.

[1] The Boyalashka reka has predominantly rain feed with high water in autumn and winter.