Reports investigations of the thawing effect of water on permafrost in northern Mackenzie District during Apr 1961. Holes were drilled under the center of a small, shallow lake with a mean bottom temperature higher than 32 degrees F and at various distances to the west of the lake. Hand probings were made near the edge of the lake, soil and water samples taken, ground temperatures measured, altitude and various terrain surveys made. It was found that the sediments below the center of the lake were unfrozen to bedrock; but the position of the permafrost table rose progressively toward shore and the thawing effect was confined to the ground lying under the lake. The thermal effect of the lake however, extended for some distance beyond.