The Moselle is 560km long (including 39km in Luxembourg), stretching from the Vosges mountains to Koblenz where it joins the Rhine, and the quality of its water has improved in recent years. Although it is much cleaner than the Seine, its quality remains "mediocre", says Alexandra Arendt, a biologist specialising in the aquatic environment at the Natur&ëmwelt association. Although her organisation does not work specifically on the Moselle, but rather on the Syre, which flows into the Moselle at Mertert, the aquatic environments researcher has a good grasp of the river's ecological issues and raises concerns about water pollution. "The Moselle is a very different river from others. It is no longer considered a natural area, but rather a navigable waterway, since it has been canalised for over 60 years now", she stated.

And this transformation of the river into a navigable waterway has had a significant impact on its ecosystem and the biodiversity it harbours. "The changes to the waterway, and in particular the installation of locks--we have two in Luxembourg--have had an impact on the river's ecological continuity. Fish passes have been installed, but they are not suitable for all species", explained Arendt. She pointed out a number of factors that are less favourable to biodiversity, such as the flow of the river, which has an impact on fish fauna, and the lack of shade, which also impacts the environment. Not to mention the fact that "some species that couldn't handle it any more have disappeared" as a result of boat traffic. Today, it is difficult to imagine making the Moselle more 'natural', but efforts are being made to make it passable for certain migratory fish, such as salmon and eels. And to improve water quality, too.

Nitrogen and phosphate pollution

"Regular analyses are carried out on all the country's rivers. They look at biology, the presence of insects, vegetation, the presence of plankton, hydromorphology and physical chemistry," said Arendt. She said that water quality has indeed improved in recent years, thanks in particular to the construction of new wastewater treatment plants. But other sources of pollution remain, and are more difficult to combat in her view, "such as mixed water discharges and sewers, diffuse nitrogen and phosphate pollution, pollution linked to the warm period, which causes the presence of blue-green algae--cyanobacteria--as well as road traffic, erosion, agriculture and the use of certain products".

As a result, the Moselle is a river with "rather mediocre" water quality. But this is not the case everywhere: "upstream of Epinal, for example, in the Vosges, not far from where it rises, the Moselle still has very good water quality, probably also because it is not channelled there", said the biologist.

The International Commissions for the Protection of the Moselle and Saar (CIPMS) is responsible for water management and protection. This cross-border organisation implements measures to improve water quality. Last year, the Max Prüss laboratory boat, owned by the German state of North Rhine-Westphalia, took samples from the river. In particular, it took samples of quagga mussels (dreissenes), a species that is a good bio-indicator of the state of the water.

Despite its current poor quality level, the government is not ruling out exploiting it for human consumption. Once it has been treated, of course. This is an avenue that is considered interesting and has been mooted for some years now as a way of meeting the country's drinking water needs. Today, 121 m3 of water from the public drinking water network is consumed every day. But the country's demographic growth is increasing this need for drinking water, and according to the Ministry of the Environment, which we interviewed on the subject, "modelling predicts risks of shortages during the peak consumption period, by 2035-2040". 

Not to mention climate change, which is leading to periods of drought and lower groundwater recharge. In reality, to secure the country's drinking water supply, the government's strategy is based on three pillars: securing existing resources, making water savings and looking for new resources. The Moselle would be one of these, "provided that it is treated in an appropriate and proven way, as is already the case abroad. This is feasible, as is the supply of treated water to distribution networks nationwide". In fact, the coalition agreement signed by the government of Luc Frieden (CSV) states in black and white that "work on a drinking water treatment plant for the Moselle will be speeded up".

Another argument in favour of this project is, once again, linked to climate change: "The Moselle, being a large catchment area, has the advantage of being less subject to climatic fluctuations", the Ministry of the Environment stated. According to the outline of the project as currently envisaged, it would involve installing a water treatment plant for the Moselle, for distribution in the southeast of the country and as far as the Sebes network.

Realisation hoped for around 2035-2040

The recommended treatment for this project would be "a multi-barrier type of treatment, making it possible to eliminate a wide range of substances in order to meet strict drinking water quality standards. More detailed studies will have to identify the most appropriate treatment technology", said the ministry. Examples from neighbouring countries illustrate the process used. In the Paris region, for example, the Seine water purification plant at Méry-sur-Oise combines advanced techniques such as ultrafiltration, ozonation and the use of activated carbon to treat the water and guarantee its quality. In the Düsseldorf region, the Rhine is also used as a source of drinking water. In this case, the water is first pre-treated, then injected into groundwater before being pumped up again and treated for distribution.

In Wallonia, near Liège, water from the Meuse is treated at the Lixhe plant, using processes such as membrane filtration and UV disinfection. Another example can be found in Geneva, where water from the Rhône is treated at the Vessy plant using various methods: coagulation, flocculation and filtration. In reality, it's not necessary to go that far. In the Grand-Est region, Metz's drinking water comes partly from the Moselle, after treatment at the Pontiffroy plant in Moulins-les-Metz.

According to the Ministry of the Environment, the project could come to fruition "by 2035/2040, depending on the increase in drinking water requirements". Following the feasibility studies already carried out, which "have led to the conclusion that using water from the Moselle is feasible in principle and represents the best existing option for guaranteeing a back-up drinking water resource. The task now is to identify a water supplier and put in place the next administrative, financial and technical steps". In the meantime, the trend is to save water, against a backdrop of global warming that is raising concerns about the future of rivers, with an impact on their temperature and water levels.

At the end of August, for example, water levels on the Rhine were low, disrupting boat traffic and therefore the economy. The Moselle may also be exposed to low water levels. But it is more the rise in water temperature that is currently creating risks, such as the development of blue-green algae and cyanobacteria.

Read the original French-language version of this report