Global studies suggest that small artificial waterbodies are widespread emitters of carbon dioxide (CO2) and methane (CH4). Farm dams are recognised as an anthropogenic system by the IPCC that must be accounted for in national emission inventories, yet data is extremely limited for irrigated landscapes. This study surveyed 37 on-farm irrigation dams across horticulture and broadacre cropping in the Murrumbidgee valley of NSW, Australia, to get a baseline of their greenhouse gas (GHG) impact. Carbon dioxide, CH4, and nitrous oxide (N2O) were measured in spring before the irrigation season, and in summer during the irrigation season. Overall, 51% and 73% of irrigation farm dams were acting as sinks for CO2 and N2O, respectively. Total CO2-equivalent emissions were highest in spring (0.44 g CO2 m-2 d-1), of which CH4 contributed 90%. Linear mixed effect models revealed that CO2 was primarily driven by dissolved oxygen (DO), ammonium, and sediment carbon content. Nitrous oxide was best explained by an interaction between DO and ammonium, and farm dams <0.001 km2 showed strong N2O consumption. Methane did not display any relationship with typical biological variables (e.g., DO, nutrients, temperature) and instead was related to soil salinity, trophic class, and size. Compared to global averages, irrigation dams had considerably lower CH4 emissions (35 kg ha-1 yr-1) than the IPCC emission factor (EF) of 183 kg CH4 ha-1 yr-1 for constructed ponds and had a lower indirect N2O EF of 0.06% compared to the IPCC default EF for rivers and lakes (0.26%). This study demonstrates that the carbon footprint of these irrigation dams is smaller than expected from the current literature on small artificial waterbodies and should be considered in future revisions of national emissions accounting.