ABSTRACTThe variability in ice conditions over a lake and between lakes is studied. The effect of snow and snow drift on ice growth is theoretically discussed and quantified. Heat flow from the lake water to the underside of the ice and melting from the upper surface are also discussed quantitatively. Observations of spatial variability in late February and early March are reported from eleven lakes in central Sweden. The standard deviation of total ice thickness for many of the lakes is only 1 cm. The highest deviation reported is 5 cm. However, the distribution between white ice and black ice shows a larger variation. White ice tends to form more extensively near shores and black ice more extensively in central parts of lakes. When ice thickness over four years on five lakes in a river basin is compared, it seems that the total ice thickness from one single lake is fairly representative of lake ice cover in a region.