To determine if the variability in basin morphometry can be the primary factor causing interbasin differences, we examined the thermal structure of Trout Lake, Wisconsin, during summer and winter stratification and quantitatively explained the observed differences in temperature among basins. Differences in hypolimnetic temperature during summer stratification and differences in the temperature of the entire water column in the winter were primarily due to the morphometric differences among basins. During winter, variations in the temperature among basins were also influenced by interbasin exchange and differences in groundwater inputs. Therefore, this multibasin lake can provide the opportunity to test the morphometric effects without the confounding inter-lake dissimilarities encountered when examining different lakes. -from Authors