On Friday, a mysterious foamy substance was spotted in the Moselle river from Grevenmacher to Schengen.

Traces of the foam were found throughout the Moselle river, from the locks in Grevenmacher to Schengen in the south of the country, all the way down the Germany-Luxembourg border.

A team from the Water Management Administration (AGE) was dispatched to take samples from different sites. The origin of the foam was found to be upstream from Schengen. 
The Moselle-Saar international warning and alert plan was triggered,requesting clarification from the French authorities.

A response was obtained from the French authorities, attributing the presence of white foam to a process caused by the natural degradation of plants. "Voies navigables de France" (VNF), the French waterways authority, regulates the water level in different basins for about 30 km before the border. This causes green algae to rise to the surface and gives an effect of white foam heading towards Luxembourg, and this effect has no proven risk