Coastal erosion affects several beaches worldwide in association with natural and human pressures. In recent decades, the coastland located on the Paraíba do Sul River mouth has been recognized as one of the main areas that suffer from this geomorphological dynamic. Furthermore, the scientific literature, even if scarce, has pointed out that these dynamics are causing negative socio-environmental responses and making the area less resilient. In the last few decades, hundreds of homes and other urban structures have become debris due to erosion caused by sea ingression, triggered by the coupling of environmental processes and dynamics occurring at different spatial and temporal scales. Thus, the present research aimed to analyze how the anthropic changes carried out in the Paraíba do Sul hydrographic basin are related to the intense coastal erosion at the mouth. Variations in fluvial–marine hydrosedimentary dynamics triggered this due to the construction of dams to supply large cities and for agricultural purposes. Water and sediment samples were collected and analyzed in different sectors of the main channel and on the adjacent coast, mapping land use in the basin area and surveying socioeconomic data. The results suggest that human pressures on the hydrographic basin during the last century are directly associated with the imbalance of the environmental system and, consequently, the progression of coastal erosion on the Paraíba do Sul delta shoreline.