Estuaries in Southeast Australia formed when fluvial valleys were flooded when sea level rose approximately 120m during the Holocene Marine Transgression (HMT) between 11-7ka (Sloss et al., 2007). However, estuarine geomorphology has developed under relatively stable sea levels for the last 1-2k years (Sloss et al., 2007). Anthropogenic sea level rise (SLR) may have drastic impacts on suspended sediment supply and morphodyanamics in estuaries by the end of the century. Understanding how estuaries have responded to past sea level changes is a key step to making informed management decisions in the context of athropogenic SLR. Westernport Bay is a large estuarine embayment on the coast of Victoria, Australia, which experienced both a Holocene marine transgression (11-7ka), and late Holocene marine regression (5-3ka). An exploration of the Holocene depositional unit in Westernport Bay was conducted to understand the sedimentary and paleoenvironment response of a large bedrock-controlled estuary to changes in sea level throughout the Holocene.