We investigated the plant cover of the small river Kueksha (Ostrovskiy District, Kostroma Region). Flora of the river comprises 2 species of macroscopic algae, 10 bryophyte and 57 vascular plant species, 69 taxa in total. The vegetation is composed of coenoses of 21 associations belonging to 8 classes according to the Braun-Blanquet system. Overgrowing is low (10–20 %), generally fragmentary. Classified by the prevalent plants and communities, most of the Kueksha River belongs to the Batrachium and Batrachium-Potamogeton botanical types. Macrophytes are a key primary producer in the river. The effect of flow regulation on the plant cover was analyzed – the rheophilic component decreased, the role of nonspecific, semiaquatic and shoal species and communities rose, overgrowing and productivity increased towards the dam. Rare plants and phytocoenoses have been found. A conclusion is drawn about sufficiently good ecological state of the river and negative influence of regulated flow.