ICPR – International Commission for the Protection of the Rhine


Plankton are mostly microscopic small organisms floating in the water. In big rivers, plankton is an important part of the ecosystem. The major share of aquatic vegetation here consists of single-celled algae, the so-called phytoplankton. If they strongly develop, they lead to the well-known eutrophication and impact the water quality.

An excessive development of plankton algae indicates too high nutrient contents in Rhine water. Such „eutrophication“ may in particular develop in the downstream section of the Rhine or in Lake IJssel.
In a river such as the Rhine the development of plant plankton is not only influenced by nutrient content, but even stronger by flow velocity and other physical and hydrodynamic factors.

Within the framework of the ICPR Rhine Monitoring Programme Biology, the phytoplankton has been sampled at regular intervals along the entire length of the Rhine since 1990 according to comparable criteria.
With the survey in 2006/2007, the programme was for the first time adapted to the requirements of the EC Water Framework Directive (WFD) according to Annex V and extended to a 6-year cycle.

Overall, the results on phytoplankton in the Rhine and its tributaries indicate on the one hand further decreasing algal biomasses in spring and thus an improvement of the trophic status. On the other hand, the conspicuous summer algal blooms demonstrate that the trophic potential for high algal biomasses is present in the Rhine as well as in its tributaries (in 2018 in the Moselle and Lahn) and can be used by different phytoplankton species. Long-term future monitoring will show whether this was an isolated case in an extremely dry and warm year or whether climate development will promote such algal blooms in the future and thus counteract efforts to improve the trophic status of the Rhine.

Learn more about the phytoplankton in the Rhine and read ICPR technical report no. 273 (available in German, French, and Dutch).

Did you know ...

that plant plankton is the basis for all life in water?

It is also known as phytoplankton and, in the Rhine, mainly consists of diatoms and cyanobacteria.

It serves as nutrition for zooplankton. In the Rhine, this zooplankton mainly consists of protozoans and rotatorias; in the Delta Rhine, copepods such as water flea and Cyclops also occur.