In spite of being known as a cleaner source of energy, large hydropower reservoirs are found that they emit a considerable amount of GHGs. Quantifying and mitigating the impact of GHGs are essential as they contribute to global warming. Cloud-based tools like GEE and G-res, Earth Observation Data, and in-situ reservoir water level have been used to quantify methane (CH 4 ) emissions from Maithon reservoir, Jharkhand, India. Mitigation techniques and developing an alternative energy source from the emission were also discussed. Initial analysis showed that a 30 cm increment in operating level could reduce CH 4 degassing emissions by 5.87±1.43%. The present workflow can be used for preparing emission baselines from large reservoirs to strengthen hydropower policy to accomplish the SDGs.