Age structure, sex ratio and shell mass of a recently introduced bivalve Anodonta woodiana (Lea) were analysed in three sampling sites at its only locality in Poland – the cooling system of two power plants near Konin (C Poland). The youngest population is that in the lake Licheńskie, the oldest individual (6+) was found in the population inhabiting the warmest canal. In the material examined, the most numerous individuals were those aged three years (43%), followed by four years (33%) and five years old (12%) individuals. The shell mass (Sm) was positively correlated with the individual age, the highest shell mass increment being observed in specimens aged 2+, 3+ and 4+. No dependence was found between the Sm parameter and sex. The shell mass varied widely (V% > 30). The highest Sm values were found in individuals from the initial cooling reservoir, the lowest in those from the lake Licheñskie, the respective water temperatures during the summer stagnation being 33 and 30°C. Except for the population from the lake Licheñskie, the sex ratio was 1:1.