The range and activities of microbial enzymes present in lake water were assessed directly in cells concentrated by tangential flow filtration. A total of 108 enzymes were assayed in this study, which included tests for 60 peptidases, 20 oxidases, and 10 esterases, and 18 miscellaneous tests. In general, no trends in the range of enzymes were associated with trophic status of the lakes. However, one lake that was hypereutrophic had a greater range of enzymes than the other lakes tested. An increase in total enzyme activity (activity/mL) was recorded with an increase in trophic status of the water. The relationship between the physical and chemical attributes of each lake and microbial enzyme activities was investigated by principal component analysis. Quantitative changes between lakes in 11 of the 21 variables were shown to be closely related to changes in the enzyme activities of the lakes; total organic carbon, particulate carbon, particulate nitrogen, pH, and chlorophyll a showed the closest relationships.