Field observation along the Coppermine River valley has revealed extensive deposits related to the presence of a major lake in late-glacial time. Numerous deltas determine a water level at approximately 360 m above sea level (asl). It is proposed that this former lake be called Glacial Lake Coppermine. Air-photo interpretation indicates that the valley was dammed by a glacial lobe covering the lowlands north of Coppermine Mountains and Dismal Lakes. During a high phase, the lake drained westward through the Dismal Lakes system to a high-level Great Bear Lake. Organic material, found in sediments infilling a river channel cut into deltaic sediments resting on top of a thick varve sequence, has yielded two 14C dates: 8400 ± 80 (GSC-2959) on wood at the base of the channel and 3210 ± 60 (GSC-2998) on peat at the top of the fill.