10Microtidal estuaries in Mediterranean climates are particularly vulnerable to the effects of 11 anthropogenic degradation. This study provides the first data on the fish and benthic 12 macroinvertebrate fauna of Hill Inlet, the northernmost estuary in south-western Australia. 13Sampling was conducted in June 2019 (Austral winter), when water levels were very high due 14to recent heavy rainfall and the bar at the mouth of the estuary was intact. Surface salinities 15 were oligohaline and declined along the longitudinal axis, ranging from 12 to 3. A marked 16 halocline was present at most sites, resulting in pronounced hypoxia. High water levels 17 precluded the use of a seine net at some sites to sample the nearshore fish fauna, however, two 18 species were recorded (Pseudogobius olorum and Acanthopagrus butcheri), both of which 19 complete their life-cycle within the estuary. Deeper, offshore waters, sampled using gill nets, 20 yielded only four species (Mugil cephalus, A. butcheri, Adrichetta forsteri and Pomatomus 21 saltatrix), due to the bar at the mouth of the estuary being closed prior to sampling thus limiting 22 recruitment from marine species. Ten benthic macroinvertebrates species were collected, 23 representing mainly polychaetes, molluscs and crustaceans. The low number of species was 24 likely caused by the hypoxia present throughout most of the bottom waters. Although these 25 data represent a benchmark against which future changes can be detected, it is recommended 26 that additional sampling is conducted when water levels are lower and the bar has been open 27 to provide a more holistic assessment of the fauna of Hill Inlet. 28 29Running head: Fish and invertebrate fauna of Hill Inlet 30