To-date Australia has had mostly coastal occurrences in a small but growing number of species of high pathogenicity avian influenza (HPAI) H5N1 clade 2.3.4.4b. The potential impacts of expected spread are the focus of significant preparation activities. Here we report on early surveillance undertaken in 2025-26 in the Murray-Darling Basin, Australia’s largest river system, which contains internationally important wetlands that support large multi-species aggregations of waterbirds vulnerable to mass mortality. We detected two low pathogenicity avian influenza (LPAI) viruses of Australian origin in wild waterbirds. Ongoing surveillance will aid in early detection and rapid response in the case of a major inland outbreak of H5N1.