Supraglacial lakes (SGLs) are ubiquitous along the margins of the Greenland Ice Sheet (GrIS) during summer. By absorbing and storing energy and facilitating heat exchange between the atmosphere, lake water, and underlying ice, SGLs enhance lake-bottom ablation and contribute to ice-sheet mass loss. However, this potentially important contribution remains poorly quantified due to the lack of lake-bottom ablation observations. In this study, we estimated lake-bottom ablation of SGLs on the GrIS and the associated melt feedback using a distributed SGL model evaluated against satellite observations. Experiments in typical catchments reveal that the lake-bottom ablation volumes ranged from 2–6×10^-3 km³ and the maximum rate reached 160 mm day^-1. Lake-bottom ablation rates increased exponentially with rising air temperature and responded more rapidly than surrounding firn/ice melt rates. Lake-bottom ablation contributed more than 30 % of the lake volume growth, and SGL melt feedbacks increased the mean catchment melt rate by 12 %–19 % relative to the all-ice baseline. Our findings emphasize the critical role of lake-bottom ablation in amplifying surface melt over the GrIS under continued climate warming.