Water temperature in water bodies, such as rivers, lakes, and reservoirs, is one of the most fundamental aquatic environmental factors that affect water quality and ecosystem. Lakes located in high altitude area are considered to be sensitive to global warming. In this study, we carried out detailed field measurements on water temperature and meteorological condition in the Tuni Reservoir in Bolivia Cordillera. Heat balance in this area is different from that in low altitude areas like Japan because the low atmospheric pressure decreases sensible heat transfer between the water body and atmosphere. By the analysis of the detailed field data, water temperature changes in the reservoir were successfully reproduced. The river water temperature in the Tuni reservoir catchment was also analyzed, and the transition of river water temperature along the river channel was discussed.
