In the spring and summer of 2016, Daniel Shugar and colleagues witnessed an act of piracy in Canada’s Yukon Territory. The Kaskawulsh River hijacked the Slims River, stealing much of its supply of water and dramatically reshaping the region’s drainage.The ongoing retreat of the Kaskawulsh glacier in the St. Elias Mountains spurred this rarely seen process of “river piracy.” For years, meltwater from the Kaskawulsh glacier has fed two large lakes at the glacier front; those lakes feed the Slims and Kaskawulsh rivers. Previously, most of the water flowed northward via the Slims River and into a watershed that ultimately empties into the Bering Sea. A lesser amount flowed southward via the Kaskawulsh into a watershed that empties into the North Pacific Ocean.Roles reversed in spring 2016—that’s when pilots first informed Shugar, a geomorphologist at University of Washington-Tacoma, that the Slims River was running low and the Kaskawulsh River was flooded. Shugar and colleagues visited the site in August, and that’s when the magnitude of the change “really sunk in.”The river piracy is visible in this image pair, acquired with the Operational Land Imager (OLI) on Landsat 8. The false-color images combine observations of shortwave infrared, near-infrared, and red light (OLI bands 6, 5, 4) to better distinguish areas of water (dark blue) from the surrounding landscape. Vegetation is green, and snow and ice are light blue.