This paper describes a new method of determining the anisotropy of aquifers contiguous with lakes. The method is based on the observed rate of decline of seepage flux with distance offshore and on the thickness of the aquifer. Deviations from an exponential decline in seepage rate with distance offshore give a measure of aquifer heterogeneity and, consequently, an estimate of the reliability of the anisotropy determination. A simple formula, derived as an analytical solution of a steady state two-dimensional groundwater flow equation, makes it relatively easy to calculate anisotropy ratios from field measurements of seepage flux through lake beds and a small number of boreholes. The importance of the anisotropy ratio in controlling the offshore distribution of groundwater and solute movement into lakes is discussed.