A consequence of the current global warming is rising sea level as polar ice melts. The future effect of such sea level rise on shorelines, river deltas and river long profiles is not well known. The problem may be understood by studying the consequences of Holocene sea level rise after the last glaciation. The melting of the Pleistocene glaciers caused a sea level rise of-120 m, mostly in a period of 12, 000 years. Here the effect of rising sea level on river deltas and long profiles is explored numerically for the Fly-Strickland River System, Papua New Guinea. The results suggest that (1) this river delta experienced the autoretreat and autobreak phenomenon during the sea-level rise, (2) the effect of the sea-level rise has extended to the far upstream reaches of the river delta, and (3) the present Fly-Strickland estuary represents the traces and on-going processes of the recovery from the effect of the past rapid sea-level rise.