<p>Assessing ecosystem health in tropical reservoirs requires integrative approaches that capture biological responses in association with physicochemical conditions. In this study, a multimetric ecosystem health assessment framework was developed and applied to evaluate the spatio-temporal ecological status of a tropical reservoir in Southern India. The framework integrates six indicator groups such as fish assemblage structure, fish production, plankton diversity, macrophyte coverage, abiotic water quality, and anthropogenic disturbance, across three reservoir zones (lacustrine, transitional, and riverine) and four seasonal periods. The composite health index indicated an overall good ecological condition (mean score, 63.2%), with pronounced spatial and seasonal variability. The riverine zone exhibited the highest ecological integrity, while transitional zones showed moderate degradation associated with cumulative anthropogenic pressures. Seasonally, ecosystem health peaked during the monsoon and declined markedly during summer, reflecting hydrological stress, elevated temperature, and reduced dissolved oxygen. Fish assemblage and production metrics emerged as the most sensitive indicators of ecosystem condition, whereas abiotic parameters remained relatively stable. The study demonstrates that multimetric frameworks provide a robust and sensitive tool for diagnosing ecological stress in tropical reservoirs and offer practical insights for adaptive fisheries management, habitat restoration, and climate-resilient water resource planning.</p>