The Sydney rock oyster (Saccostrea glomerata) is an iconic Australian native species of great commercial and ecological significance. Amid debate over aquaculture, the role of the S. glomerata industry in safeguarding Australia’s estuaries has been overlooked. This paper explores how, for over 150 years, S. glomerata has been central in monitoring, understanding and protecting one of NSW’s greatest assets, our estuarine ecosystems.