Bottlenose dolphins are long lived and known to bio accumulate inorganic and organic pollutants, including toxicants such as PFAS. The health of apex species such as dolphins may make them suitable as indicators of their ecosystem. The health of animals may be affected directly through pollutants or indirectly, by disrupting the overall ecosystem, such as in eutrophication. Legacy and contemporary toxicants have been found in Adelaide’s Port River estuary, which also is home to a population of bottlenose dolphins. Dolphins in Port River estuary have been studied since 1988. The study has documented longitudinal changes to dolphin abundance and distribution, apparently in response to changes in local ecosystem. Photo identification has established individual home ranges for frequently sighted individuals. Collaborations with marine mammal biologists and veterinary pathologists have revealed toxicant loads, diseases and genetic abnormalities in individuals known to be resident in the estuary. A recent outbreak of an unknown wasting disease has killed several young male dolphins, all of whom had identical home ranges. Multidisciplinary investigations are seeking to determine if localised pollution or other cause may be responsible for the deaths. This presentation will discuss the Port River dolphins as indicators of ecosystem health.