β-Galactosidase activity of Escherichia coli was investigated in response to long-term starvation, changes in temperature and the presence of certain nutrient sources in lake water. β-Galactosidase activity decreased markedly in filtered-autoclaved lake water at 25°C and 37°C, whereas it remained almost constant at 4°C and 15°C for 60 days. Increases in β-galactosidase activity were observed in response to the following nutrient sources: glycine, serine, methionine and ammonium sulfate at 4°C; glycine and ammonium sulfate at 15°C; glycine, serine, methionine and ammonium sulfate at 30°C. Glycine addition led to an increase in β-galactosidase activity of almost five and seven orders of magnitude at 15°C and 30°C, respectively. In addition, L-methionine had the strongest influence on b-galactosidase activity, which was detected as an increase of seven and eleven ordersof magnitude at 4°C and 30°C, respectively. The effect of several amino acids and other nitrogen sources depended on the concentration of the nutrient source and the temperature. The results showed that, in lake water, long-term starvation, temperature change, and variationsin nitrogen sourcesalter β-galactosidase activity. Those effects should be taken into account when monitoring coliformsfrom the environment.