At this time Port Jackson, Broken Bay and Port Hacking were deep bedrock valley downs which freshwater streams ran. As the ice-sheets melted after the last glacial maximum, the sea-level rose, covering the continental shelf and flooding the valleys to form the present day saltwater estuaries of Port Jackson, Broken Bay and Botany Bay (V.Attenbrow,2002).

As the sea level rose at the end of the glacial maximum it deposited sand barriers across the river mouths and formed parabolic dunefields on the headlands (V.Attenbrow,2002).

Prior to its inundation from the rising sea level starting about 9000 years ago, the base of Botany Bay was a swampy sand plain across which the earlier channel of the Georges River flowed in a southerly direction to join the Port Hacking River.