Formation and sudden drainage of glacial lakes pose increasing hazards in high-mountain regions, threatening downstream communities, infrastructure and ecosystems. Accurate bathymetric reconstruction and lake volume estimation are crucial for flood modeling, hazard assessment, and monitoring climate-driven glacial lake dynamics. This study uses a recently drained lake at the margin of Gornergletscher, Monte Rosa Massif, Western Alps, to reconstruct its bathymetry and estimate its volume by combining a high-resolution digital elevation model (DEM) from low-cost uncrewed aerial vehicle (UAV) imagery with multispectral Sentinel-2 data. The UAV data were used to generate an orthomosaic and a high-resolution DEM of the empty lake basin. Lake extents corresponding to five filling stages, together with the DEM, enabled pixelwise depth estimation, yielding a mean lake depth for maximal filling of 21.94 m and an estimated corresponding water volume of 0.298 ± 0.11 × 10⁶ m 3 . Field observations indicated direct glacier contact and subglacial drainage through vertical conduits. Sentinel-2 also revealed smaller lakes in 2017 and 2018. Comparative analysis of climate variables from lake (2017, 2018 and 2022) and no-lake (2019–21) years highlighted higher April–June temperatures as the dominant factor controlling lake formation. This study demonstrates the value of integrating UAV three-dimensional (3-D) terrain modeling with satellite remote sensing for high-resolution glacial lake monitoring.