A vast icy landscape on the western Greenland ice sheet is crisscrossed by turquoise rivers and dotted with meltwater lakes in late July 2015. A recent study of the hydrology of the ice sheet shows how the shifting network of streams and rivers that form during the melt season can transport water from surface of the ice to the ocean. Greenland loses ice to the sea mainly through two processes: the shedding of icebergs from glaciers that run into the sea, and surface melt runoff. A handful of studies have mostly focused on Greenland's massive meltwater lakes, which can disappear in a matter of hours. But rivers sinking into holes in the ice are the main conduit for transporting water from the top of the ice sheet to the bottom. Besides contributing to sea level rise, melt water runoff also accelerates ice loss: when the water percolates through the ice sheet and reaches the rock below, it slightly lifts the ice, helping it flow faster toward the ocean.