Mangrove forests are vital coastal ecosystems that provide a range of ecological, economic, and protective services. However, these ecosystems are increasingly threatened by anthropogenic activities, particularly in resource-rich regions like Rivers State, Nigeria. This study employed Geographic Information System (GIS) and remote sensing techniques to assess the spatio-temporal changes in mangrove forest cover in selected Local Government Areas (LGAs) Gokana, Andoni, Asari-Toru, and Degema from 1995 to 2024. Multi-temporal Landsat satellite images were analyzed using supervised classification to delineate land use/land cover (LULC) categories including mangroves, freshwater vegetation, built-up areas, and water bodies. The results revealed a significant and progressive decline in mangrove coverage across the LGAs, with Gokana and Andoni experiencing a 59.49% loss, and Asari-Toru and Degema a 42.67% loss over the study period. Conversely, built-up areas and freshwater vegetation expanded considerably, indicating growing urbanization and possible ecological succession. The findings strongly suggest that human-induced activities such as infrastructure development, oil exploration, and land reclamation are the primary drivers of mangrove degradation. This study underscores the urgent need for targeted conservation strategies, sustainable land-use planning, and strengthened environmental regulations to preserve the remaining mangrove forests and restore degraded areas.