This study reconstructs environmental conditions at Mill Creek, within the lower Hawkesbury-Nepean Valley, by the use of fine resolution palaeoecological studies of sediments. Archaeological surveys and historical accounts are used to investigate ecosystem response to known human activities. Research found that during prehistoric times (between 820 BP and the 1790s), the study area was well vegetated with dry sclerophyll communities on the valley sides, and a highly productive wetland community occupied the moist valley floor. Valley sides were generally stable, and little fire was evident in the landscape. Sediment was mainly deposited on the valley floor from the Hawkesbury-Nepean River during flood. After European settlement in the 1790s, sedimentation rates and charcoal preserved within sediments increased significantly, probably due to agricultural and clearing practices, both locally and upstream. Consequently, vegetation communities were altered. In 1967, the study area became part of Dharug National Park. Forestry and agricultural activities were excluded from the catchment, and the fire regime was reduced in frequency. Present-day vegetation communities appear to be becoming more like those that prevailed during prehistoric times. However, sedimentation rates remain elevated due to continued disturbance to the greater Hawkesbury River catchment. Recent poor water quality, coupled with a succession of floods on the Hawkesbury River, has increased wetland productivity levels, and their spatial extent, at Mill Creek.