We collected water samples from the river surface using a pre-rinsed HDPE 1 L bottle. Temperature and electrical conductivity were measured by using a CTD (Conductivity, Temperature, and Depth) SonTek Cast Away device (accuracy: 0.05 °C and 0.1 PSU). In winter the device was submerged beneath the ice surface for a minimum of 10 seconds to let the device adjust to the temperature before being steadily lowered to the riverbed and pulled up again. During the ice-free period, the CTD was lowered into the water from the dock, when the dock was moved out. Otherwise, the CTD was cast into the river from shoreline. The mean temperature and conductivity were additionally recorded on written protocols. For the pH/EC measurements, the originally frozen, unfiltered samples were thawed and measured at the AWI Laboratory in Potsdam. A pH/EC AR Robot from Seal Analytical was used for the measurements in combination with a Thermo Scientific Versa Star Pro meter, a pH electrode (Thermo Scientific Orion), and a conductivity electrode (DuraProbe 4-Electrode Conductivity Cell) with a measuring range of 1 µS/cm to 200 mS/cm. A three-point calibration was performed for pH measurement.