Vliet Clean (S)up

The Vliet Clean (S)up took place between the 24th and the 27th of August. During the clean-up, the Vliet river has been cleaned of plastic and other trash between Leiden and Delft. Children from multiple youth scouting organizations supped down the river in 4 days and picked up all the plastic they could find. During the clean-up WaterLab, together with The Ocean Movement, researched the amount of microplastics in the water. Along multiple sections, we tested a new method to do measurements and take samples, to see how much microplastics we find in the Vliet.


In the final week of the 2021 summer holidays a 4-day Vliet Clean (s)Up is organized, from Leiden, via Leidschendam-Voorburg and The Hague, to Delft. During this week, every day, youth members of local scouts will sup (paddle board) a part of the track and collect all the trash and plastic from the river Vliet. Every day, in collaboration with multiple organizations, there are a diversity of side events for 75-100 children at the different scouting-locations, focusing on the themes of watersports and plastic soup. Children can follow workshops and paddle board to collect trash, do water experiments and make toothpaste without micro plastics. During the event, WaterLab is doing a research pilot for a new methodology for collecting and measuring micro plastics: the so-called 5-Gyres sampling-method. Together with foundation The Ocean Movement and with the help of participants of the Vliet Clean (s)Up, we will investigate how we can monitor micro plastics in our water in a more accessible and affordable way.


Microplastics: In total we measured 10 sections, using 2 trawls. The number of microplastic particles found, are extrapolated to the number of particles per kilometer. Based on the particles we found, it was calculated that on average there are 83.417 particles/km present in the Vliet! Most of the microplastics were found inside and just outside Leiden (3 section with 127.745, 203.593 and 337.625 microplastic particles per km). 47,7% of the particles are fragments (that have broken off from larger pieces of plastic), 34,6% foils (packaging materials) and 11,7% styrofoam.

Macroplastics: In collaboration with Noria the amount of macroplastics found by the suppers has also been analyzed. The entire route was sectioned up, to see if some parts contained more plastics then other parts of the route. Over the course of the 4 days of the Vliet Clean (s)Up, 1341 parts of plastics (102,2 kg!) were cleared from the water. The largest part (23,2%) consisted of food packaging, followed by Styrofoam (13,1%). Additionally, there is a clear connection between the population density and the amount of plastic found along the route: the more people, the more plastic.


Taking consistent samples of micro plastics in fresh water is still in development. Our plan is to do a pilot study during the cleanup for using a modification of the 5-Gyres sampling-method (a trawl at the water surface for catching micro plastics), made suitable for use behind a sup or paddling board. This will be the first step towards developing a good and sound citizen science monitoring strategy for micro plastics in fresh water.

Foundation The Ocean Movement will use their experience to build two modified 5-Gyres Manta trawls. During the cleanup we will involve groups of children to train and use their own smaller DIY-trawls to also collect micro plastics and analyze them.


The goal of the cleanup and the micro plastics pilot is to map how much and what types of plastic float around in the Vliet and of course to clean up as many of it as we can. So far, there is no good ánd affordable method to do micro plastics research without doing analyses in a lab to measure the amounts of micro plastics. With this research we hope to develop a method that affordable ánd reliable, so that micro plastic research will be possible in many more locations.


Sandra de Vries – WaterLab
Maarten Erich – The Ocean Movement

This research is made possible because of the Tauw Foundation, Waterschapsbank, Rabobank and Delfland.

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