The use of carp herpes virus (CyHV-3) as a biocontrol agent for carp is arguably the best chance Australia has to common carp, a notorious aquatic pest. However, prudent use of such an agent requires potential risk be assessed along with potential benefits. Low dissolved oxygen and high concentrations of oxygen are two potential risks from mass carp mortality. Impacts of carp decay were examined in bucket experiments, 720L ponds, 1000L mesocosms and in an2.5ha wetland. Oxygen depletion was strongly influenced by temperature and it took approximately half the time at to deplete oxygen to anoxia in experiments at 20ºC than at 12ºC. The oxygen demand at 20ºC was 0.799 mg/kg/min. Mesocosm experiment revealed that high phytoplankton productivity in response to nutrient enrichment can lead to supersaturated oxygen concentrations during the day, but the additional oxygen demand from decaying carp can lead to periods of anoxia. Six tonnes of dead carp were added to a 2.5ha wetland to simulate a mass mortality event. Biological oxygen demand increased to 80 mg/L and periods of anoxia were observed. Results from these laboratory and field trials are being incorporated into a coupled hydrological and biogeochemical model in order to predict the oxygen and biogeochemical response to carp mortality in different aquatic habitats around Australia. It can be concluded that there is a water quality risk associated with decaying carp carcasses. How this risk manifests in reservoirs, wetlands and the River Murray will depend upon the carp density, the prevailing flow and temperature. Key environmental and infrastructure assets may need protection from the water quality challenges. This work will support the National Carp Control Plan and assist with planning for the water quality risks that could be expected with mass carp mortality upon release of carp herpes virus CyHV-3.