This dataset contains diel hydrological and in-situ hydrochemical measurements collected at three sites along the Wiesent karst headwater stream in northern Bavaria, Germany, between 21 and 22 August 2023. Parameters include location information, stream width and depth, discharge, water temperature, pH, electrical conductivity, and dissolved oxygen. Measurements were conducted at 4 h intervals over a 24 h period to assess short-term hydrochemical variability along the spring-to-stream transect.