The growth response of common duckweed Lemna minor was studied at various temperature and pH levels for its possible application for remediating eutrophic waters. The dry weight, chlorophyll a, nitrogen, phosphorus, potassium, peroxidase (POD), catalase (CAT) and malondialdehyde (MDA) levels were determined. Whilst optimum growth was recorded at between 20 and 30 °C, reduced growth and an increase in protective enzymes were noted at both lower and higher temperatures. There was oxidative damage at temperatures of less than 10 °C and greater than 40 °C. The pH of the growth medium was inversely related to the growth responses of Lemna minor. At acidic pH and at temperatures between 20 and 30 °C, the environmental conditions were most suitable for phytoremediation of eutrophic waters. Under these conditions, and when harvested regularly, Lemna minor may be of use in counteracting eutrophication.