Four large subglacial lakes aligned along a large tectonic boundary in Dronning Maud Land have recently been linked to the onset of Recovery Ice Stream, the largest ice stream draining into the Filcher-Ronne Ice Shelf. While these lakes appear to be stable, new analysis of ICESat altimetry data has identified four active lakes under the fast flowing part of the ice stream and captured the movement of subglacial water through these lakes. Over the ICESat observation period (October 2003-April 2007) water appears to be migrating downstream and ponding in the lowermost lake, causing changes in surface elevation of ~7.5 m. The water origin may either be melting in the Recovery catchment resulting from basal melt of the ice sheet by geothermal heat or frictionally-induced melting beneath the ice stream. An estimate of the catchment melting at 1mm/yr may account for much of the elevation change in the downstream lake.