Between Germany and the Netherlands, the Rhine is on average three degrees warmer than 100 years ago. Ecologists warn of serious consequences for nature and wildlife.
Power plants are the main reason for the warming
Parts of the river reach an alarming 28 degrees Celsius (82 Fahrenheit) during summer with the warmest temperatures measured between the cities of Mainz and Worms, said researchers.
A new study released by environment group BUND says the development is partly caused by global warming, but mostly by waste water pumped in by nuclear and coal-fired power plants that channel water off to cool the facilities and then pump it back into the main river.
"The waste heat from all German power plants would be enough to warm every single building in the country," say Joerg Nitsch of BUND.
"This gigantic waste of heat that the Rhine has to deal with shows how utterly inefficient producing electricity with coals and nuclear power is," he added.
Salmon population endangered
Environmentalists warn that temperatures have risen by three degrees Celsius since the early 20th century.
The change is particularly dangerous for nature and wildlife in the river, especially for the salmon population which the government is trying to reintroduce to the river. Salmon is known to not swim up a river to spawn if the water temperature exceeds 25 degrees Celsius.
BUND is urging that no additional power plants be built along the river and says a concrete plan is needed for regulating and limiting the warming of the Rhine.
Editor: Kate Bowen