Surface melting on the Greenland Ice Sheet is common up to ∼1400 m elevation and, in extreme melt years, even higher. Water produced on the ice sheet surface collects in lakes and drains over the ice sheet surface via supraglacial streams and through the ice sheet via moulins. Water delivered to the base of the ice sheet can cause uplift and enhanced sliding locally. Here we use ice-penetrating radar data to observe the effects of significant basal melting coincident with moulins and calculate how much basal melt occurred. We find that more melting has occurred than can be explained by the release of potential energy from the drainage of surface meltwater during one melt season suggesting that these moulins are persistent for multiple years. We find only a few persistent moulins in our study area that drain the equivalent of multiple lakes per year and likely remain active over several years. Our observations indicate that once established, these persistent moulins might be capable of establishing well-connected meltwater drainage pathways.