This study estimated the tourism carrying capacity of St. Mary’s Island (SMI), which is located on the west coast of India. The analysis is based on threshold values for environmental factors, biophysical properties, socio-economic aspects and management features. SMI features two primary beaches used for recreational activities such as swimming, sunbathing, relaxation, geo-tourism and water sports. The occupancy and vacancy rates related to the island’s carrying capacity were assessed under various scenarios. This study evaluated the island’s carrying capacities across three key types: Physical Carrying Capacity (PCC), Real Carrying Capacity (RCC) and Effective Carrying Capacity (ECC). The results indicate that the current tourism activities are operating below the real carrying capacity, suggesting potential for sustainable expansion. Further, we reviewed 641 web-based entries and collected 50 onsite tourist reviews for site insights. Overall tour satisfaction, services, environmental conditions and management features within the study area were incorporated as key factor in our evaluation. The results revealed that tourist satisfaction levels range from good to excellent at 69%. Additionally, insights from tourist reviews shared on various social media platforms can also serve as baseline data for enhancing ecotourism in the region. As a result, this study can provide valuable information for stakeholders, such as decision-makers, planners and ecologists in order to facilitate the sustainable management of island resources and the development of ecotourism. Sustainable tourism and eco-friendly infrastructure development further reduce anthropogenic nutrient and pollutant inputs, supporting the restoration and maintenance of natural biogeochemical cycles. This integration supports sustaining marine ecosystem functions crucial for biodiversity, fisheries, climate regulation and the long-term sustainability of ecotourism and coastal livelihoods.