Τhe aim of this study was to check the water quality of Aposelemis Dam reservoir. The water quality was studied in nine (09) different water depths: 0 m, 02 m, 03 m, 05 m, 07 m, 09 m, 10 m, 13 m and 15 m. A sudden change in the temperature of the water was observed at the water depth of 7 m (thermoclinic phenomenon) and a change in pH (from pH> 8 to pH <7.5) at the depth of 3 m. At greater depths we identified a sharp increase in metal concentration, as well as prevalent solubility (Mn, Fe, etc.). Relating to microbial load, it was much lower in depths > 2m, compared to 0-2 m. As the depth increases the Total Organic Carbon (TOC) decreases in contrary with the nutrient concentration (N, P) which increases. Color and odor values appear elevated in depths greater than 5 m.