• Lake Vioreau is the largest freshwater reserve in Loire-Atlantique.
  • The 180-hectare body of water has just been emptied to allow work to be carried out on its dam.
  • Many curious people have been flocking to the site for a few days.

"It's really too weird! It looks like a lunar landscape. Strongly that the water returns. Séverine knows Lake Vioreau well, a site where she comes "at least once a year to the beach or even sail." But if she "struggles to recognize" the scenery, it is because the huge lake located in Joué-sur-Erdre (Loire-Atlantique), north of Nantes, has been emptied. Almost entirely. More than 7 million m3 of water were evacuated naturally, for several weeks this winter, to allow the necessary work to be carried out on the dam.

For a month, the "emptying" has been completed. The large reservoir of Vioreau, 4 kilometers long, seems nothing more than a huge field of sand, mud and small pebbles. Some pontoons and stranded boats testify to a nautical past not so old. Only a thin area of water remains on the south side, near the dam. "It's still a funny sight. We don't see that every day," says Jérôme, camera in hand. "It seems much bigger without water", considers Xavier who does not "regret having made the trip"...

"There are risks of getting bogged down, it's dangerous"

Thanks to the good weather and "word of mouth", dozens of curious people flock to the site every day. They sometimes venture far, even if it means returning with their feet rubbed, or even putting themselves in danger. "The floor is loose in places. There are real risks of getting bogged down. There are also pockets of water with risks of drowning, especially when darkness arrives. It's dangerous. We put warning signs but it's not enough," observes Jean-Luc Séchet, vice-president of the Loire-Atlantique departmental council, owner of the lake. The desire to enjoy the show is such that some walkers have even "moved the barriers" that hindered the footpath on either side of the dam under construction.

The other problem with this influx of visitors is the environmental protection of the riverbanks. "We are in a Natura 2000 area. The ecosystem is extremely fragile. There is, in particular, a small plant, the delicate beetle, which is unique in Loire-Atlantique and must be protected. Its trampling worries us, "warns Jean-Luc Séchet.

Replenishment in one year

Unfortunately for treasure lovers, the drying up of the lake has not given rise to any particular discoveries. "We have not found old objects, nor original elements, assures the elect. It must be said that the last oil change dates back 20 years. But there may be things in the sludge removed during the cleaning of the eastern part that will be done during the summer. About 25,000 m3 will then be extracted and spread on agricultural land. The intervention will improve water quality.

The restoration work on the dam, which aims to consolidate the structure built in 1835, must continue until the end of autumn 2023. The refilling will then be carried out in winter, "thanks to the rain", for several months. Some of the 40 tonnes of fish moved in November will be reintroduced. Cost of the overall operation for the Loire-Atlantique department: 13 million euros.

The main freshwater reserve of Loire-Atlantique, Lake Vioreau and its dam had been built at the request of Napoleon I, with the aim of guaranteeing continuous navigation on the canal from Nantes to Brest. Its primary function is still indispensable, especially in times of drought. The lake hosts a leisure center with different water activities.

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  • Pays de la Loire
  • Nantes
  • Road repairs
  • Dam