Aim: To determine the survival of Escherichia coli O157:H7 in dairy wastewater from on-site holding lagoons equipped with or without circulating aerators. Methods and Results: Survival was monitored in dairy lagoon microcosms equipped with or without scale-size circulators. Both laboratory strains of E. coli O157:H7 and an isolate of E. coli H7 from wastewater had poor survival rates and none proliferated in water from waste lagoons with or without circulators. Furthermore, the decline of E. coli O157:H7 was not enhanced in those microcosms equipped with circulators. Strain variation in survival was observed in both circulated and settling waters. The decline rate of E. coli O157:H7 Odwalla strain increased proportionately with the inoculum load. Escherichia coli failed to establish itself in wastewater even after four sequential inoculations simulating continuous faecal input into the lagoon. The native aerobic bacteria survived longer with a decimal reduction time of 21.3 days vs either introduced or native E. coli, which declined rapidly with decimal reduction time of 0.5-9.4 days. Conclusions: Escherichia coli O157:H7 failed to establish and proliferate in dairy wastewater microcosms equipped with or without circulating aerators. Significance and Impact of the study: This study furthers our knowledge of pathogen survival in wastewater, and suggests that proper management of wastewater before its use in irrigation is essential to reduce pathogen transfer to crops.