Acknowledgements

We thank J. Jokela, F. Pomati and F. Altermatt for discussions regarding experimental design, and J. Jokela, M. Hoyer, M. Reyes, S. Käser and G. Siegrist for help in setting up the experiment. We also thank D. Steiner for laboratory analyses of chlorophyll for the sensor calibrations. Furthermore, we would like to thank C. Ebi for installing the sonde-grid on site at Dübendorf. This work was supported by a Strategic grant from Eawag and a project grant from the Swiss National Science Foundation to P.S. (grant no. 310030L_166628), and to B.W (grant no. 206021_157750). M. Lürig was funded by the Center for Adaptation to a Changing Environment (ACE) at ETH Zürich, and by Eawag.