[1] The river takes its source at an altitude of 1,743 m in the Batak Mountain of western Rhodope mountain range, 1.3 km west of the Kartela locality on the road between the towns of Batak and Dospat.

Until the town of Peshtera it flows in a north-northeastern direction in a deep, at places canyon-like, valley which widens only in the area around Batak.

At the village of Byaga the valley of Stara Reka widens once again, winds around the Besaparski Hills from the south and east and enters the Upper Thracian Plain, where the river flows into the Maritsa at an altitude of 183 m west of the town of Stamboliyski.

[1] Its drainage basin covers a territory of 350 km2 or 0.66% of Maritsa's total[1] and borders the drainage basins of the Chepinska reka and several small tributaries of the Maritsa to the west and northwest and the Vacha to the east and south, all of them right tributaries of the Maritsa.

There are six settlements along its course: the towns of Batak and Peshtera and the villages of Byaga, Isperihovo, Kurtovo Konare and Novo Selo.