Seagrass meadows provide vital ecosystem services and functions but have suffered widespread declines, therefore requiring active restoration. In Australia, emerging ecological restoration standards offer promising guidelines for planners and practitioners, yet their application to seagrass remains challenging, with rare success typically limited to small-scale projects. In South Australia, a remarkable natural recovery of more than 11,000ha of Posidonia meadows has been recently identified –a temporal and spatial scale never witnessed before, offering valuable insights for informing restoration guidelines and improving large-scale success. However, the mechanisms driving this recovery remain unknown. This study combines genomic tools and numerical modelling to investigate the recovery processes, by assessing local and regional colonisation mechanisms through population genetic analyses and particle dispersal simulations. Field surveys and genomic barcoding identified both Posidonia sinuosa and Posidonia angustifolia as the main leaders of the recovery, despite their slow growing capacities. In addition, environmental modelling suggests that P. sinuosa recovery was more prevalent in calmer waters, while the more wave-resistant P. angustifolia recovery dominated in exposed areas. Ongoing analyses are exploring the modes of recovery and the potential sources of recruitment. These findings highlight the possibility for the success of large-scale restoration over decades with two slow-growing seagrass species.