The Island of Unguja in Zanzibar (Tanzania) has experienced accelerated urban development growth since early 90s`. These rapid land demands put additional stress on the country's ability to rebuild urban canters, cities and management of natural forest resources. The purpose of this study was to determine the impact of urbanization on groundwater catchment area at Masingini-Mwanyanya catchment forest reserves from 1992 to 2022. The study used remote sensed change detection approach to determine the Land Use Land Cover (LULC) changes under three decades of (1992 to 2022). Landsat images of 1992, 2002, 2012 and 2022 were used to determine these changes. In addition, paired samples t-test was conducted to determine the significant changes in mean population growth, urbanization and humidity. Results revealed that forest catchment areas have been decreased by 14.5% (i.e. from 8.3 km2 in 1992 to 7.1 km2 in 2022), while built up area has increased from 0 km2 in 1992 to 1.7 km2 in 2022 (indicating that the catchment area has been encroached at a rate of 0.05 km2/year). Further results showed an existence of undesirable LULC evolution (i.e. persisted changes from forest to build up areas), posing significant threat and risk to the sustainable management of water resources and catchment forest reserves. The paired t test revealed a significant (at p ≤ 0.05 or 95% confidence) changes of the urbanization, deforestation and humidity. Based on these results, the study recommended for more studies and upscaling of the existing findings, collaboration of the responsible authorities in intervening, re-demarcating and gazetting the new Masingi-Mwanyaya forest catchments area aiming to allow a sustainable use of groundwater resources.