The Australian government is considering employing the koi herpesvirus (KHV) for biocontrol of invasive common carp (Cyprinus carpio) in the Murray–Darling river system of southeast Australia in 20181,2. KHV is on the World Organisation of Animal Health (OIE) list of notifiable diseases3, yet the biocontrol programme has been framed as a safe and manageable proposition1,2. Previous reports highlight that viruses have been successfully employed in the biocontrol of terrestrial vertebrates1, including cats on Marion Island, and feral rabbits in Australia and New Zealand. However, compared with the biocontrol of terrestrial vertebrates, the biocontrol of large, highly fecund aquatic animals such as carp adds novel risks.