Tengchong County, Southwestern China, is a renowned volcanic region with abundant geothermal resources. This study systematically investigates the geochemical characteristics of hydrothermal waters in Tengchong, utilizing major and trace elements as well as hydrogen and oxygen isotopes. The primary objectives are to identify the potential sources of the hydrothermal waters and provide a detailed assessment of heavy metal pollution, with a particular focus on fluoride. The results of δD and δ