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 β-galactosidase activity, which was detected as an increase of seven and eleven orders of 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 variations in nitrogen sources alter β-galactosidase activity. Those effects should be taken into account when monitoring coliforms from the environment. © Springer-Verlag and SEM 2002.