Meltwater drainage through glaciers strongly influences ice dynamics and related hazards, yet detailed observations of active englacial and subglacial networks remain scarce due to challenges in direct observation. We present a novel high-density, UAV-based 3D ground-penetrating radar (GPR) survey of Switzerland’s Otemma Glacier, integrated with dye tracing experiments, photogrammetry and hydraulic potential modeling, to map internal water pathways with unprecedented spatial resolution and cover