A study on physico-chemical dynamics of Temengor Reservoir was conducted to determine whether headwaters and seasonal changes play a major role in regulating physico-chemical dynamics of Temengor Reservoir. Temengor Reservoir receives water from its surrounding water catchments and headwaters. Then, the water flows into a series of hydroelectric dams, namely the Bersia, Kenering and Chenderoh dams. Generally, water quality in Temengor Reservoir can be classified as Class I. Physico-chemical trends showed that water quality in euphotic zone of Temengor Reservoir is stable and consistent. Two-way ANOVA analyses showed that seasonal variations only affected water temperature, Secchi disc’s depth and nitrate-nitrogen. Based on Tukey’s post-hoc test, all three headwaters in this study exert no influence to the reservoir’s water quality. These insignificant differences were probably due to water temperature and the size of the headwaters and the reservoir itself. In situ parameters profiling showed that the epilimnion zone in Temengor Reservoir is from the surface to 6 m depth, the metalimnion zone is from 6 m to 12 m depth and the hypolimnion zone is from 12 m depth onwards to the bottom of the reservoir. Thus, continuous water profiling monitoring that covers high and low water levels need to be conducted to determine characteristics of the physico-chemical dynamics in the water column and also to analyse changes in reservoir layers. Through these studies, discontinuity trends in the Perak River could be determined and suggestions to the respective agencies could be made to conserve and to sustain downstream biodiversity. A study on physico-chemical dynamics of Temengor Reservoir was conducted to determine whether headwaters and seasonal changes play a major role in regulating physico-chemical dynamics of Temengor Reservoir. Then, the water flows from its surrounding water catchments and headwaters. into a series of hydroelectric dams, namely the Bersia, Kenering and Chenderoh dams. Generally, water quality in Temengor Reservoir can be classified as Class I. Physico-chemical trends showed that water quality in euphotic zone of Temengor Reservoir is stable and consistent. Two -way ANOVA analyzes showed that Seasonal variations only affected water temperature, Secchi disc’s depth and nitrate-nitrogen. Based on Tukey’s post-hoc test, all three headwaters in this study exert no influence to the reservoir’s water quality. These insignificant differences were probably due to water temperature and the size of the headwaters and the reservoir itself. In situ parameters profiling showed that the epilimnion zone in Temengor Reservoir is from the surface to 6 m depth, the metalimnion zone is from 6 m to 12 m depth and the hypolimnion zone is from 12 m depth onwards to the bottom of the reservoir. monitoring that covers high and low water levels need to be conducted to determine characteristics of the physico-chemical dynamics in the water column and also to analyze changes in reservoir layers. Through these studies, discontinuity trends in the Perak River could be determined and suggestions to the 各 agencies could be made to conserve and to sustain downstream biodiversity.