The study focuses on short-term changes in surface water temperature in Polish lakes, and is based upon the experimental measurements of water temperature conducted every 60 minutes during the years 1971–2015. 19 lakes were selected on the grounds of their morphometric properties. The examinations were carried out in the system of expeditionary measurements (up to 8 days) and stationary measurements (over 2 months), and included temperature of surface water and its vertical distribution. The analysis of the results showed that temperature differences of water (daily amplitudes) were observed in both time and spatial distribution. The biggest differences in water temperature occurred during spring warming, and often reached 4–5°C, while rarely exceed 2°C in the remaining periods of the yearly cycle. The mean day value occurs twice; in the morning between 8:00 (7:00 GMT) and 11:00 (10:00 GMT), and in the evening at 20:00 (19:00 GMT) and 22:00 (21:00 GMT). Daily changes in the vertical distribution of water temperature are clearly visible down to the depth of 2.5–3.5 m, whereas are just perceptible to the depth of 5.5–7.0 m.