The water of Stanwell-Fletcher lake, on Somerset Island, is essentially isothermal, with melting of ice only in the summer and only along the edges. Sedimentation is very slow because of the short season of inflow and the low organic activity. Silty sand derived from river bed loads accumulates on shallow marginal deltas and shelves. The sediment is poorly sorted because ice cover prevents wave action and removal of the fine material to deeper water. Mud, derived largely from river suspended loads, settles slowly in the central part of the lake. Faint laminae in the shelf sediments may be varves, but the deep water mud is structureless. The oxidation-reduction boundary in the sediments is at 5-20 cm, deeper than in temperate lakes, because of oxidation at the lake bottom and slower reduction within the sediment.