Lake Donjek was a large reservoir formed when Donjek Glacier dammed Donjek River. Although the basin is empty at present, a minor advance of Donjek Glacier could again dam the river and impound approximately 234 × 106 m3 of water. Ice-dammed lakes are commonly unstable, giving rise to destructive floods called "jökulhlaups," or glacier outburst floods. Our aim in this paper is to estimate the likely magnitude of outburst floods from Lake Donjek so that the danger to downstream installations can be assessed.In attempting to estimate the maximum discharge from Lake Donjek, we use both the empirical formula of Clague and Mathews and a computer simulation model based on theoretical contributions by Nye. The September 1967 outburst flood from Summit Lake, B.C. is taken as a reference event against which predictions of the simulation model are compared. Our estimates for peak discharge from Lake Donjek lie in the range 677–5968 m3 s−1 with values in the range 3968–5968 m3 s−1 being considered most probable.