The Australian lungfish is one of only five surviving lungfish species in the world and is likely the oldest living vertebrate on the planet with fossil records dating back 380 million years. At one time there were at least seven species of lungfish whose distributions extended to the center of the Australian continent, but at present native populations of the Australian lungfish persist in only Burnett and Mary Rivers. Despite being a federally listed threatened species, globally recognized as a scientific icon and sacred to the indigenous people of the region, the long-term persistence of the Australian lungfish is in severe jeopardy. Aquatic habitats supporting the core distribution of lungfish have been modified and degraded by decades of human activities. Our proposal contributes new scientific knowledge necessary to stop the decline of, and support the recovery of, the endangered Australian lungfish. We are providing the first ever investigation of century-long trends in lungfish trophic ecology by using innovative stable isotope analysis of carbon and nitrogen in different regions of fish scales coupled with radiocarbon scale-aging techniques. This will allow for an unparalleled glimpse into how resource utilization by lungfish (which can live for more 80 years) has responded to extensive river impoundment in the Burnett River and a long-history of agriculture land-use in the Mary River. This is an innovative approach that will provide direct management recommendations in terms of riparian vegetation restoration and dam operations, and thus will help guide conservation actions to ensure the future of the world's oldest living vertebrate.