High temporal resolution temperature measurements were analysed for 5 neighbouring lakes in the English Lake District to assess how the diel range in epilimnetic temperature varied among the lakes. These lakes experience the same climate but differ morphometrically, allowing lake-specific drivers of diel variability to be determined. The magnitude of the diel temperature cycle was calculated as the difference between the measured maximum and minimum daily epilimnetic temperature. Our analysis demonstrated that the magnitude of the diel temperature cycle was primarily influenced by the depth of the upper mixed layer. The magnitude of the diel temperature cycle was lowest for the largest lake, Windermere South Basin, which varied by approximately half that of the smallest lake, Blelham Tarn. A significant correlation between the diel temperature range and lake area was observed in the summer months caused by the larger lakes typically experiencing higher wind speeds, which in turn lead to greater mixing depths and thus to a lower diel temperature range. Water temperature has a major effect on lake biology and biogeochemistry, so it is important to recognise its variability in different lake types.