Biofilters in Lake Geneva: Investigation

Lake Geneva is currently experiencing a substantial pollution of biofilters, the first evidence appeared in spring 2012. Surfrider Foundation Europe is committed to the investigation to discover the cause and origin of the pollution. The investigation has shown its quality, especially through the Chapter collaboration of the Basque Coast and Lake Geneva, as well as the European Headquarters in Biarritz.


Biofilters were discovered in Lake Geneva in spring 2012, but the person responsible never alerted anyone of the pollution, in fact it would have been surprising if he had! The pollution was reported first to Francois Verdet from the Basque Coast Chapter in January 2013, who is well practiced in the issue having already dealt with Biochips in Aquitaine in 2010. He immediately engaged with volunteers from the Lake Geneva Chapter. The two Chapters are investigation due to this invasion, however this lake, said to be “the cleanest in the world”, has two other known pollutions (phosphate levels higher than the standard CIPEL and an alarming rate of micro-plastics).

Two types of biofilters have already been identified: with no possible confusion as, one is flat and circular and the other thick and square. The Basque Coast Chapter discovered soon enough that the wastewater treatment factory “Saillon” and “Evolène” had incidents resulting in the release biofilters, in January and March 2012. Satisfactory results but not complete since biochips used by these two stations are circular…What about the squares biofilters?


A stranger in the ranks of biofilters, the appearance of square biofilters interests and provides an opportunity for Charléric Bailly  from Surfriders headquarters in Biarritz to compile their identity file: manufacturers, use, etc., the more you know about the pollution the better you can track it. At the same time, a call to witness is launched on social networks by Gaël Bost, Lake Geneva Chapter: “We were able to create a map updated daily in real time of areas affected by pollution on the whole of Lake Geneva to get a “snapshot view” of the lake and affected zones”. With the testimonies of Surfrider supporters, the Lake Geneva Chapter comes quickly to the conclusion that the Swiss banks are not the only ones affected, the southern shore of the lake with the villages of Anthy, Sciez, Thonon, St. Disdille and Lugrin were particularly plasticized by these square biofilters.

The volunteers from Lake Geneva contacted every wastewater treatment factory on the French coast: by noting the purification processes, they are certain that the source is not French. Here begins the start of a long process: “I went on the field, checked every beach and the amount present in an attempt to find the tributary which had transported the filter medias. After having found come upstream of the lake, I thought they came from the Rhone. So I was to meet three wastewater treatment factories, a refinery and a waste incinerator on the plateau upstream of the Rhone hoping to find the source of the pollution, still nothing”… Thus still nothing, but Surfrider doesn’t admit defeat that easily.


The answer however is located in their shape…square. Information gathered at the Surfrider headquarters in Biarritz determines a Swiss provider of square bio filter media. Finding the supplier is a big step and can lead to identify clients of square media in the geographic area, however, due to required professional confidentiality, industries will not provide such information … unless you have sufficient authority to receive it. Gaël contacted the responsible districts of Vaud and Valais because, they, had more details. Very interested by the issue since the incidents of Evolène and Saillon, the investigation continues: the supplier told those responsible of the districts the name of the wastewater treatment factories using this type of biofilters on Lake Geneva. This square shape is less common and the name Saint-Prex stands out.


After several months, the responsible who spilled a huge number of square biofilters in Lake Geneva was finally identified. Gaël met with the head of the wastewater treatment factory in Saint-Prex, the engineering and the equipment that performed the installation of these biofilters, the investigation ends but no action: “we contacted the rangers who are in charge of investigative work to determine if it was necessary to prosecute the polluters. The investigation therefore continues for them. Now that we have the assurance that the biofilters can no longer be dumped in Geneva, we are working with municipalities to schedule clean-ups of the affected beaches. This will take time because the number of beaches involved is important.“.

For its part, headquarters in Biarritz continues to conduct research on various types of filter media and techniques used: leaks like Lake Geneva can be avoided if there is correct utilisation of the bio filter media. The most common cause is the overflow basin, with bio filters in the absence of being stirred, get clogged in the disposal gates, and raise the level of water. This can be avoided: Surfrider Foundation Europe establishes recommendations for use in the future to avoid this kind of pollution, which unfortunately will remain permanent.

Alban Derouet, Environmental Editor

Translated by Charlotte Williams

One thought on “Biofilters in Lake Geneva: Investigation

  1. shay erismann

    Since 2014 Plages Propres is finding square and circular biofilters every cleanup along Haut Lac sites form Montreux to La Tour de Peilz. Additionally an abundance of cotton swabs (Qtips) and plastic shotgun shell wads.


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