The Sredetska reka (Bulgarian: Средецка река) is a 69 km long river in southeastern Bulgaria, which flows into Lake Mandrensko, itself draining into the Black Sea.

Some 2.5–3 km from the source, the river flows northeast through a vaguely defined valley with very oblique slopes, covered with oak forests.

After the confluence with the Chetmanska reka, the river enters a 50–60 m wide hilly valley with shrubs along the rights banks.

Further downstream, the river enters a very steep narrow valley with almost vertical slopes of 80–85°, overgrown with thick bushes and thorns.

In the lower course of the Sredetska reka downstream of the village of Belila, its valley becomes very wide with an indistinct transverse profile.

After the town of Sredets, the river enters section of 1–2 km with strongly curved meanders that reach all the way to the village of Debelt.

At its mouth at Lake Mandrensko the width of the river is about 25 m and the depth about 0.80 m, with low swampy banks and muddy bottom.