In 1990, the freshwater wetlands and mangroves near Wyndham, north-west Australia, were Ramsar-listed due to their ecological importance. To understand wetland formation and stability over time, two sediment cores from the King River and one from the Parry Lagoons wetlands were analysed using sedimentological and palynological techniques. During postglacial sea-level rise, mangroves extended across all sites and were supported by enhanced freshwater input. Between 7.4 and 6.3k cal a BP the mangrove forest contracted, probably driven by sea-level stabilization, and hypersaline mudflats, reflecting the onset of drier climatic conditions, developed along the King River. After 6.3k cal a BP mangrove diversity declined, probably linked to peak dryness around 4k cal a BP. The Parry Lagoons wetlands are at least approx. 600 years old and their development is probably related to an increase in effective precipitation since approx. 1k cal a BP. The region's mangroves could be considered relatively stable under changing climate as they are still present today, although reduced in biodiversity and areal extent. The early phases of development of the Parry Lagoons freshwater systems cannot be resolved but given the character of these wetlands, freshwater input appears to be the vital driver of ecosystem functioning.