In the winding journey of 22 waterways through Poland, Germany, the Netherlands, Belgium, and France, the 58-year-old Frenchman collected samples of water for scientific analysis.
In all, Christophe Gruault rowed more than 2,000 kilometres (1,240 miles) over 48 days.
"The Polish part is the most pristine and the cleanest with areas that are protected and respected by people," he said.
"In Germany's east, you feel that people have taken root in nature without degrading it."
Researchers at the National Museum of Natural History in Paris, which has supported the trip, will study Gruault's samples and observations.
"It will be interesting to... see whether the cities have any consequences on the treatment of pollution," Denis Duclos, the museum's director of European and international relations, had previously said to AFP.
Pollution in Poland's rivers came into the spotlight last year when nearly 250 tonnes of dead fish was recovered in July from the Oder River that runs through Poland and Germany.
Polish authorities later said toxic algae was to blame, ruling out industrial pollution as the cause.
But German authorities called it a "man-made environmental disaster", saying the algae growth had been sparked by the introduction of salt into the waters.
Related Links
Our Polluted World and Cleaning It Up
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
