Seagrasses are crucial habitat-forming species that contribute to coastal and estuarine ecosystem health. The genetic diversity of seagrass meadows underpins their resilience and adaptive capacity to environmental change. The long-term success of restoration strategies must account for the genetic structure of source populations. Posidonia australis, endemic to temperate Australia, has experienced widespread decline and is listed as endangered in several NSW estuaries. Restoration is increasingly used to recover lost meadows, though efforts remain limited in scale and constrained by degraded donor sites and low natural recruitment. In NSW, restoration of P. australis relies primarily on naturally detached beach cast shoots. The fine-scale genetic structure of populations remain poorly understood, limiting the ability to match source material to local conditions. This study assessed patterns of genetic diversity and structure within and among four NSW estuaries across ~570 km and 4.7º in latitude: Wallis Lake, Pittwater, Port Hacking, and Merimbula Lake. We genotyped 460 samples collected from multiple sites per estuary, with individuals spaced 15–20 m apart to capture fine-scale spatial structure across gradients in depth, salinity, and temperature. Genotyping was performed using SNP markers (DArTseq), alongside environmental and morphological observations. Detached beach cast shoots collected from estuarine shorelines were also genotyped and compared to nearby meadows. Preliminary results show clear genetic differentiation among estuaries and structure within some estuaries. Genotypic diversity also varied, with some sites dominated by a few clones and others exhibiting high clonal richness. These findings suggest previously unrecognised spatial genetic structure relevant to restoration planning. Most detached fragments were locally sourced, but their genetic similarity to nearby meadows varied across sites. Identifying likely source areas can improve provenance matching and help refine collection practices. This project addresses challenges in marine restoration and explores solutions to enhance efforts and ensure continued ecosystem service provision.