Activities of the respiratory electron transport system (ETS), C uptake, chlorophyll and temperature were determined at a station in the center of Donghu Lake. Seasonal, fluctuations in ETS-activities ranged from 100 to 460μg O2 h-1.L-1. Production: respiration ratio (P/R) calculated from C uptake and ETS-activity, ranged from 0.2 to 6.8. The test on cultured algae ETS-activity revealed marked differences in different growth phases. ETS activity is suggested as an indicator of lake nutrient status. Activities of the respiratory electron transport system (ETS), C uptake, chlorophyll and temperature were determined at a station in the center of Donghu Lake. Seasonal, fluctuations in ETS-activities ranged from 100 to 460 μg O2 h-1.L-1. Production: respiration ratio (P / R) calculated from C uptake and ETS-activity, ranged from 0.2 to 6.8. The test on cultured algae ETS-activity revealed marked differences in different growth phases. ETS activity is suggested as an indicator of lake nutrient status.