Rapid sedimentation of sands, silts and muds associated with seaward prograding tidal delta and central basin deposits, characterise the early Holocene sediment infill of the Hawkesbury River's estuary. From about 6 ka BP fluvial muds and sands dominate the estuary and sedimentation rates are much reduced. Micro-fossil records contained in sediments from the middle Hawkesbury-Colo Rivers region support the sedimentological-lithostratigraphic interpretation of estuary development. Information from fossil diatoms indicates that for a period of about 300 years around 6 ka BP, there was an increased marine influence in this part of the present estuary. This may have resulted from the probable peak in the rate of relative sea-level rise, although there may also have been a contemporaneous increase in freshwater flow down the river. Pollen and charcoal records from Mill Creek, downstream from the Colo sequence, show that sclerophyll forest, occasionally with rainforest elements, became more dominant from 8 ka BP. In contrast, the upper tidal Casuarina glauca forest decreased in importance during the phases of sea-level rise and the subsequent ‘still-stand’. Together the palaeoenvironmental records show broad agreement in defining the patterns of regional environmental changes and linked phases of estuary development during the Holocene. Differences in records appear to relate to local site factors and to the limitations in provenance, persistence and resolving power of the data types. The rapid accumulation rates provide an opportunity to investigate high magnitude but low frequency events in estuarine environments, including floods and fire.