North of Nantes, the astonishing spectacle of the empty Lac de Vioreau attracts the curious

“It’s really too weird! It looks like a moonscape. Hope the water comes back. Séverine knows the lake of Vioreau well, a site where she comes “at least once a year to the beach or even to go sailing”. But if she “struggles to recognize” the scenery, it’s because the huge lake located in Joué-sur-Erdre (Loire-Atlantique), north of Nantes, was emptied. Almost entirely. More than 7 million m 3 of water were thus evacuated naturally, for several weeks this winter, in order to allow the necessary works to be carried out on the dam.

For a month, the “drainage” has been completed. The large reservoir of Vioreau, 4 kilometers long, seems nothing more than an immense terrain of sand, mud and small pebbles. A few pontoons and stranded boats bear witness to a not so ancient nautical past. Only a thin surface of water remains on the south side, near the dam. “It’s still a funny sight. You don’t see that every day,” wonders 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 coming back with dirty feet, or even putting themselves in direct danger. “The ground is loose in places. There are real risks of getting bogged down. There are also pockets of water with the risk of drowning, especially when it gets dark. It’s dangerous. We put up warning signs but that’s not enough”, observes Jean-Luc Sechet, vice-president of the departmental council of Loire-Atlantique, owner of the lake. The desire to enjoy the show is such that some walkers have even “moved the barriers” that blocked the footpath on either side of the dam under construction.

Boats stranded during the drying up of Lake Vioreau, in Loire-Atlantique. – F.Brenon/20Minutes

The other problem posed by this influx of visitors is the environmental protection of the banks. “We are in a Natura 2000 zone. The ecosystem is extremely fragile. There is, in particular, a small plant, the delicate coleanthus, which is unique in Loire-Atlantique and which we must protect. Its trampling worries us, ”warns Jean-Luc Séchet.

Replenishment in one year

Unfortunately for treasure lovers, the drying up of the lake did not lead to any particular discoveries. “We did not find any old objects, nor original elements, assures the chosen one. It must be said that the last oil change dates from 20 years ago. But there may be things in the sludge removed during the cleaning of the eastern part that will be carried out during the summer. About 25,000 m3 will then be extracted and spread on agricultural land. The intervention will improve water quality.

Restoration work on the dam, which aims to consolidate the structure built in 1835, must continue until the end of autumn 2023. Water will then be replenished during the winter period, “thanks to the rain”. , For many months. Part 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 reserve of fresh water in Loire-Atlantique, Lake Vioreau was developed at the request of Napoleon I, with the aim of guaranteeing continuous navigation on the Nantes-Brest canal. Its primary function is still essential, especially in times of drought. The lake hosts a leisure center with various water activities.

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