Between 1978 and 2011, the average water temperature of the Rhine has increased by 1 to 1.5 °C. The figure indicates the number of days per year with water temperatures above 22 °C for three Rhine monitoring stations on the German-Swiss border at Weil, near Karlsruhe and near Koblenz.
Climate change and further rising air temperatures will continue this development (see ICPR Technical Report No. 209). In addition, industry and energy production have permissions for thermal discharges.
The extreme heat period in the summer of 2003, e.g., combined with low flow led to an extraordinary warming up of the Rhine and its tributaries (see ICPR Technical Report No. 151).
During particularly warm summer periods combined with low flow water temperatures may rise to such an extent that negative effects may appear in the ecosystem (see ICPR Technical Report No. 204).
Water related provisions limit thermal discharges from water uses. If water temperatures in the Rhine or its tributaries rise above 28 °C, no additional thermal discharges will normally be allowed.