Temperature
For the two main study systems, Lake Skrukkebukta and Lake Vaggatem, daily water temperature measurements were available from an automated datalogger at the Skogfoss hydropower plant situated 25 km upstream from Lake Skrukkebukta and 23 km downstream from Lake Vaggatem. We calculated annual mean water temperature, mean summer temperature (Jun-Jul-Aug) and mean autumn temperature (Sep-Oct-Nov) from the logger data. Mean annual water temperature has increased significantly by 0.3°C per decade (p<0.01, F=9.3611,25, adj-R2= 0.243, Appendix Table S4), mean autumn temperature (September-November) has also increased significantly by 0.4 °C per decade (p<0.01, F=11.261,26, adj-R2= 0.275, Appendix Table S5), and mean summer water temperature increased (June-August) by 0.4 °C per decade (Fig. 1) (p=0.037, F=4.871,25, adj-R2= 0.13, Appendix Table S6).