Two hundred and seventy-five lakes were sampled in the summer of 1979 to assess the factors controlling susceptibility of northcentral Wisconsin lakes to acidification. In addition to direct evaluation of means and ranges of the physical and chemical characteristics, a cluster analysis was carried out using alkalinity, color, and chlorophyll a data. Three well-defined clusters emerged that appeared to be controlled by hydrology: A - dominated by surface runoff; B - dominated by groundwater; C - dominated by precipitation. Relationships between morphometric, hydrologic, and terrigenous factors that can influence lake water quality and susceptibility were further examined by discriminant analysis of 18 watershed properties across the three lake clusters. Hydrologic factors were most important in differentiating the low alkalinity and high alkalinity lakes.