During an 18-month period, heterotrophic bacteria were quantified and the rates of glucose mineralization were measured in samples from the sediment-water interface of Bethel Lake, a small productive lake located in the city of Sudbury, Ontario, Canada. Among three incubation temperatures 2°C, 18°C, and 37°C, the highest bacterial counts were obtained consistently at 18°C. With incubation at 2°C the highest counts occurred when the water temperature in the lake was 10°C or lower, and psychrophilic bacteria were recovered only at such times. Most of the 2°C and 18°C isolates were psychrotrophs. Some of the 18°C isolates were incapable of growth at either 2°C or 37°C, the extreme recovery temperatures examined. Turnover times and heterotrophic potentials for the substrate of interest were calculable for seven of the eight mineralization experiments. Substrate turnover occurred more quickly and the potential for glucose mineralization was always greater at the higher test temperature, for a given sampling. Cold water temperatures did not preclude glucose mineralization.