The Kisköre Reservoir (Tisza Lake) is the second largest standing water in the Carpathian Basin. Its water level is usually regulated artificially which creates unique habitats with high nature conservation value. The study, investigated the changes in the water quality variables in the Reservoir. A total of 19 sampling sites were sampled during the Autumn season. The water variables indeed influenced the algal composition as cynabacteria blooms were evident were there was eutrophication as the algal composition positively correlated with the water variables.