Ice thickness was measured from the bottom of the ice cover to the piezometric water level and to the top of the ice cover. Because most limnological sampling holes are drilled in low-lying areas, it was thought that ice thickness measurements were biased. Therefore, random ice thickness measurements were performed in a 1000 m^2 sampling grid on each lake in past years. Statistical analyses by Dr. Priscu have shown that measurements from three ice holes are representative of the ice thickness measured by this grid system.