Faced with the proliferation of cyanobacteria, the city of Rennes must regularly prohibit swimming in the Apigné ponds.
The municipality would like to open a bathing place in the nearby Bougrières pond, which has long been used as a sand extraction site.
The Lafarge group will soon restore the natural site which serves as a meeting place for men, but there remains a strong constraint: the collection of water.
“We have no solution for Apigné”.
After having tried everything to improve the water quality of the Prévalaye ponds, the city of Rennes gave up.
She will never be able to guarantee a place to swim here without fearing the multiple pollutions with cyanobacteria.
For years, the municipality has been forced to sign bathing closure orders because of the health risk linked to the proliferation of small blue algae which can cause nausea, vomiting and skin irritation.
"We don't have depth, the water doesn't renew itself, we can't do anything about it," says biodiversity assistant Didier Chapellon.
The neighboring agricultural activity and its regular spreading bring too much organic matter and phosphorus, asphyxiating the water of the Apigné ponds.
A water depth of more than twenty meters
For several years, the municipality has set its sights on the nearby Bougrières pond.
Located a few hundred meters away, it has a major advantage: its depth.
“At the deepest, we have a depth of water of 20 to 21 meters”, assures Claire Morice.
The land manager of the Lafarge group knows this natural site very well, which her company has been exploiting for nearly forty years.
Here, an electric barge sucked up tons and tons of sand to feed the appetite of concrete construction customers.
The career stopped in 2018 due to the constraints that had become too strong.
“There is still deposit.
But we had to give priority to the collection of drinking water.
We could not afford to suspend our activities vis-à-vis our customers.
We preferred to stop.
Because the problem is there.
If the transparent waters of the Bougrières pond offer great prospects for swimming and even light navigation, they also present a solid constraint.
Here, people come to draw water to supply the taps of the metropolis.
“The body of water is magnificent with exceptionally clear water.
The site is huge with great biodiversity.
But it's a reserve of drinking water, so we can't do anything there, ”warns Didier Chapellon.
But the idea of installing a beach on the edge of the Bougrières persists, especially since it seems to be the only credible solution for swimming.
But when ?
Not before 2023 or even 2024, the time for the Lafarge group to make the site “clean” and respect the specifications.
“On the Bougrières site,
we still have to manage the arrival of certain invasive plants such as water primrose, buddleia or Japanese knotweed.
We also have a few trails to recreate,” explains Claire Morice.
Hydrocarbon pollution in the soil
Today, the huge 80-hectare site is relatively uncrowded.
Some walkers come to venture there but it is above all a place of more or less secret encounters between men.
The municipality dreams rather of making it a spot for strolling and entertainment for families.
We are still far from it.
On the nearby site of Lillion pond, traces of Lafarge operations are still clearly visible.
An impressive pile of bitumen, an old electrical room and hydrocarbon pollution under the old mechanical workshops remain to be dealt with.
“We will also have to remove the dike to unite the two Lillion ponds,” warns Claire Morice.
To complete this file, Lafarge will have to bring in machinery and excavate the contaminated land.
Filed in March, his file is being investigated by the State services.
If accepted, you will still have to wait until 2024 to take advantage of this still little-known natural site.
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Bathing
Water
Pollution
Career
Sand
Lafarge
Brittany