Research was conducted on the number, secondary production and physiological properties of benthic bacteria in the eutrophic Lake Chełmżyńskie. It was found that the number of psychrophilic bacteria (CFU) occurring in the bottom sediments of the studied lake and the rate of bacterial production (BP) were all characterized by a distinct seasonal variability and depended on the location of the study site and the type of bottom sediments (ANOVA, p-value <0.05). The maximum total number of bacteria (TNB), CFU and BP were observed in summer. Muddy sediments were characterized by a greater number of bacteria than sandy ones. A higher number of heterotrophic microorganisms and greater rate of secondary production were found at the sites located in the part of the studied waterbody near the town than at the sites located far from the town. The most numerous benthic bacteria were strains of hydrolyse fat, protein and cellulose. The least numerous were pectinolytic and chitinolytic bacteria.