The Inner Thermaikos Gulf is located in the northwestern Aegean Sea, receiving water and sediment fluxes from the Axios, Aliakmon, Gallikos and Loudias Rivers. The geomorphological and sedimentological evolution of the system is reconstructed for the last 150 years (1850–2000), on the basis of detailed analysis of historical bathymetric charts. Late Holocene history is considered within the context of changing riverine sediment supply and human activities. Three evolutionary stages are identified. Stage I (1850–1916) corresponds to a natural phase of rapid deltaic progradation and sea-floor deposition, with an average sediment accumulation rate of 6.5 × 106 m3 a−1. During Stage II (1916–1956), human interference (e.g. artificial changes in river delta plains, realignment of channels and land reclamation schemes) to the deltaic system increased sediment delivery to the coastal waters by a factor of three; this, in turn, enhanced the progradation of the active river mouth areas. In contrast, Stage III (1956–2000) is characterized by significant coastline (deltaic) retreat and erosion of the adjacent sea floor (net loss of 2.5 × 106 m3 a−1); this was as a result of extensive river damming, which trapped a significant part of the sediment moving seaward. Furthermore, these human impacts have affected the character of the surficial sea-bed sediments of the Gulf, by reducing the proportion of mud. The response of the deltaic margin of the Inner Thermaikos Gulf to various anthropogenic interventions seems to be analogous to that of other deltas in the Mediterranean region where large drainage projects, the development of irrigation networks and dam construction have taken place within their river basins.