The success of oyster reef restoration can be enhanced by data on the distribution of remnant populations that identify suitable restoration locations. However, this data is often not available as it relies on information from historical distributions. This presents a challenge as distribution data is often collected by diver surveys that can be expensive and time-consuming. We designed a qPCR-based environmental DNA assay as a potentially cost-effective way to collect distribution data for the functionally-extinct oyster, Ostrea angasi in Port Phillip Bay, Victoria. O. angasi eDNA accumulation and decay was measured in aquaria-containing oysters in low and high densities, prior to testing the efficacy of the eDNA approach for detection of oysters at 15 field sites. O. angasi eDNA accumulated significantly faster in aquaria where more individuals were present, while eDNA became undetectable 2-6 days after oysters were removed in low-density treatments. eDNA samples were successful at detecting O. angasi in the field when taken in close proximity to an oyster population. Evidence suggested increasing the sample number and volume could reduce false negatives and maximise oyster detection. This study demonstrated the potential for eDNA to identify current O. angasi populations and inform the restoration of this functionally extinct species.