This paper describes changes in the seasonal dynamics of leaf length and count per ramet, ramet biomass and chlorophyll content in leaves of Vallisneria spiralis L. in a heated lake near Konin in the Kujawy Lake District. In the middle of summer, there was a clear decrease in leaf length, number of leaves per ramet and plant biomass. This indicated that leaves and entire ramets were being replaced at this time. Leaves of V. spiralis proved to be an excellent substrate for assemblages of epiphytic algae, which were mainly found on the distal 20-centimeters of the leaf tip. In this heated lake, V. spiralis was able to grow even at the end of October. This was attested to by the fact that the number of short, young, green leaves in ramets was higher at the end of October than at the end of September.