The Crnajka river, the shorter but natural headstream, originates from the central west slopes of the Deli Jovan mountain, and flows to the north, next to the villages of Tanda and Crnajka, in the valley between the Deli Jovan to the east and Veliki Krš and Mali Krš mountains to the west.

The river flows to the south, curving around the western side of the Liškovac mountain and the northern slopes of the Mali Krš mountain, next to the oldest copper mine in Europe and once prosperous mining village of Rudna Glava.

It meets the Crnajka in the narrow valley between the southern Liškovac and northern Deli Jovan mountains, at the village of Miloševa Kula, forming the Porečka River.

The river continues Crnajka's northerly direction between the mountains of Liškovac (on the west) and Veliki Greben (on the east).

The Porečka River drains an area of 538 km², belongs to the Black Sea drainage basin and it is not navigable.