Microalgae can synthesise the ozone depleting pollutant and greenhouse gas nitrous oxide (N₂O). Consequently, significant N₂O emissions have been recorded during real wastewater treatment in high rate algal ponds (HRAPs). While data scarcity and variability prevent meaningful assessment, the magnitude reported (0.13–0.57% of the influent nitrogen load) is within the range reported by the Intergovernmental Panel on Climate Change (IPCC) for direct N₂O emissions during centralised aerobic wastewater treatment (0.016–4.5% of the influent nitrogen load).