Ovalona karelica (Stenroose, 1897) was first discovered for the invertebrate fauna of the Voronezh region south of the main habitat. It is a rare benthic species of sladocerans crustaceans (Crustacea, Cladocera). The species was encountered among macrophytes in thickets Typha angustifolia (L.) and Potamogeton lucens (L.) in two floodplain lakes of the Khopersky Nature Reserve in summer. The explored small lakes, where the species was found, are distinguished by the peculiarity of the floodplain regime; they are flooded from the main river in medium and high water years and remain connected to each other for some time. Lake Bolshoe Podpesochnoe has an area of 2.7 hectares and a maximum depth of up to 6 m. It is characterized by a low degree of overgrowing – 25%, the distance to the river Khoper is 1.1 km, last flooding was noted in 2018. The area of the lake Maloe Podpesochnoe is 1.9 ha, the maximum depth is up to 5 m, the degree of overgrowth is 35–40%, the distance to the river is 0.9 km, the last flood was in 2018. The size of the individuals encountered was from 380 to 420 microns, the abundance varied from 90 to 550 ind./m3, the share in the total number of planktonic invertebrates was from 0.1 to 0.32%. The discovery of Ovalona karelica is associated with the specificity of its habitat conditions and small number, and this also indicates a poor study of the fauna of phytophilic and benthic invertebrates in small floodplain water bodies.