[1] The river takes its source at an altitude of 266 m from the Kapaklia spring, located in the easternmost reaches of the Sredna Gora mountain range, some 1 km southeast of the village of Staro Selo.

Throughout its whole course the Blatnitsa flows through the Upper Thracian Plain in a shallow valley.

It initially flows south, at the village of Konyovo it turns in direction west-southwest until the town of Nova Zagora, when it takes a turn to the south-southwest until its confluence with the Sazliyka at an altitude of 108 m in the southwestern neighbourhoods of the town of Radnevo.

There are five settlements along its course: the villages of Konyovo, Ezero, Bogdanovo and Lyubenova Mahala in Nova Zagora Municipality of Sliven Province, and the town of Radnevo in Radnevo Municipality of Stara Zagora Province.

Its waters are almost completely utilised for irrigation for the intensive agriculture in the Upper Thracian Plain.