A survey of several enhanced biological phosphorus removal (EBPR) plants within Australia has demonstrated that a group of bacteria known as the "G" bacteria are able to proliferate under a broad range of plant configurations. The diverse designs and operational parameters of these plants did not permit definitive determination of the factor(s) contributing to the proliferation of G bacteria. Two plants were monitored over time to assess the G bacteria and phosphorus accumulating organisms (PAO) populations in relation to key operational parameters. The mixed liquor biomass and operational parameters were compared to other plants successfully and unsuccessfully reducing phosphorus from the wastewater. Two critical factors recognised in this study were the dissolved oxygen concentration in the aerobic zone and the type and amount of carbon source in the anaerobic zone.