The study of ground frost levels in a drained and undrained forested fen showed a significant delay in thaw as well as lower temperatures at 40 and 60 cm depths in the drained area because of the insulating effect of drier surface peat in the drained area. The undrained area froze to greater depths than the drained area, but thawed more rapidly. Ice was present year-round at 16.7% of the sample points in the portion of the drained area of low hydraulic conductivity. Thickness of the frozen layer appeared to be related to hydraulic conductivity as well as drainage. Thawing from underneath the frozen layer accounted for 38% of total thaw in the undrained area.