Yambo Lagoon, located in the province of Cotopaxi, Ecuador, is a high-altitude aquatic ecosystem exposed to increasing anthropogenic pressures derived mainly from tourism and agricultural activities. These pressures threaten its ecological integrity and highlight the need for context-specific tools to support environmental management and decision-making. This study aimed to develop a set of environmental sustainability indicators adapted to the socio-ecological conditions of the Yambo Lagoon, using the Pressure–State–Response (PSR) framework. A mixed-methods approach was applied, combining quantitative data obtained through structured questionnaires administered to residents and visitors, and qualitative information derived from semi-structured interviews with local stakeholders. Descriptive statistical analysis and qualitative content analysis were conducted using SPSS v.26 and ATLAS.ti, respectively. The results indicate a high level of environmental awareness among respondents, with 87% recognizing the ecosystem’s characteristics and mass portion identifying tourism and agricultural activities as the main sources of environmental pressure. Fifteen key variables were identified across social, economic, environmental, and institutional dimensions. Pressure indicators revealed intensive land use, agrochemical application, and increased tourist flows as dominant stressors, while state indicators reflected deterioration in soil quality, water resources, and biodiversity. Response indicators showed limited effectiveness of existing management actions. The study concludes that the proposed indicator system provides a practical and replicable tool for monitoring ecosystem sustainability and emphasizes the need to strengthen environmental education, participatory governance, and integrated management strategies to ensure the long-term conservation of the Yambo Lagoon