Water and sediment supplies from ungauged areas were calculated and combined with datasets from gauging stations to establish sediment budgets. Using sediment budgets and regression relationships, the influence of the Three Gorges Dam (TGD) on downstream delivery of sediment was quantified. We found that 151 mt/yr (1 mt = 10⁶ tons) of sediment has been retained by TGD since it began operation (2003–2005). In response to this, significant erosion has occurred in the downstream riverbed. This erosion did not offset the sediment lost in the reservoir, and the sediment flux into the estuary decreased by 85 mt/yr (31%). This decrease has lead to conversion from progradation to recession in the delta front. In combination with other anthropogenic impacts, TGD was expected to decrease the sediment flux into the estuary for centuries, which is of great importance for delta ecosystem and human development.