Bike Touring Highlight
... and almost warm enough for swimming even in winter ;-)
Excerpt from the wiki on the river Erft:
Due to the hot water discharge from the lignite industry into the Erft, plant species such as the Brazilian thousand-leaf and the South American leaved water-spill can survive here. Every year, 300 million cubic meters of warmed-up groundwater ("swamp water") is pumped from the lignite mine into the Erft. In addition, there is the cooling water from the Frimmersdorf lignite power plant. In winter the mean water temperatures are still 15 ° C and in summer 28 ° C. The middle course of the river is 8 ° C warmer than the upper course. The hot water is supplied below Erftstadt. As early as the 1990s, anglers reported catching piranhas three times, which, in contrast to the sunfish, could not form a reproductive population, but were only exposed aquarium fish and probably only survived for a few months. There are also guppies and red-cheeked turtles in the Erft. For this reason, BUND tried to stop the construction of the Neurath brown coal power plant.