Captain’s striped shirt and aviator glasses on his nose, Yann Lefebvre holds the helm and the microphone to comment on the panorama. At the exit of the narrow Savières canal, 4.5 kilometers long, which starts from the Rhône, the Lac du Bourget (Savoie) reveals its majestic area of 44.5 square kilometers. Sheltered from the light breeze, inside the glazed cabin of the Savoyarda restaurant boat with seventy-five seats, you have to squint in the brilliance of this early autumn.
To the east, you can see the northern ridges of the Bauges alpine massif and Mount Revard, which dominates Aix-les-Bains, at an altitude of 1,500 meters. Towards the west, the Jura chain of the Epine plunges steeply into the water, creating a landscape of northern fjords. To the south, the combe de Savoie reveals, in the distance, the Belledonne massif, “the first to turn white in winter”, launches Yann Lefebvre. At 54, he knows every detail of the setting that encloses the largest natural lake of glacial origin in France. Embarked as a cabin boy at the age of 16 on his father’s boat and now captain of a fleet of three ships, the boatman has imprinted all the shades of color of Lake Bourget on his retina. Some have taken more than forty years to appear. “Here, we went from dark green to turquoise blue”he says, mockingly, as he begins a U-turn on the lapping of the waters.
Fishermen and boaters
It is because the Lac du Bourget has come a long way. In the 1970s, under the effect of the degradation of the quality of the water, it even came close to asphyxiation. In this stagnant environment, very sensitive to pollution, the discharge of water treated by the treatment plants of Aix-les-Bains and Chambéry causes its eutrophication: under the massive supply of nutrients, long filamentous algae proliferate. By decomposing at the bottom, on the gravel pits essential to the incubation of the eggs of certain fish, they smother the space. The survival of arctic char and lavarets, two emblematic salmonids of alpine lakes, sought-after delicacies, is threatened. “Fishermen were the first to sound the alarm: their nets were turning green and the noble fish were disappearing”explains Sébastien Cachera, responsible for the management of aquatic environments of the Intercommunity Committee for the sanitation of Lake Bourget, an organization created to save the place.
The bet made by elected officials at the time consisted in diverting purified wastewater to an environment capable of withstanding these discharges. The choice is made on the waters of the Rhône, through a 12 kilometer long gallery, dug in the Epine massif. Forty years later, the quality of the water is notably measured thanks to the rate of phosphorus, a marker of pollution, divided by 25 in four decades. “Today it is at the level of the natural state of the lake”rejoices Sébastien Cachera.
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