Stage 9: Nantua to Chambéry

We rode over the Grand Colombier last year on the way to Culoz where Jarlinson Pantano outsprinted Rafał Majka. Today, though, we end on the south end of the Lac du Bourget in Chambéry, so it’s a good a time as any to revisit one of the largest lakes entirely on French soil.


Bourget is a fairly deep lake, around 80 m on average, and as a result, it is meromictic, meaning that it doesn’t always mix vertically. Lakes develop thermal stratification as the summer sun warms the surface water, which, because it is less dense than cold water, sits on top of cooler water at the bottom of the lake. As the surface cools off during the fall, the water at the surface becomes more dense and falls to the bottom of the lake, overturning the water. This overturning is critical for biological productivity in lakes as it mixes the oxygen-rich surface waters with the nutrient-rich bottom water.


This is how stratification develops in a dimictic lake. In contrast, the Lac du Bourget doesn’t fully mix over the course of the fall and winter.

Vinçon-Leite et al. (1995) discovered that Lake Bourget doesn’t mix all the way from top to bottom in a normal winter because the lake is so deep. Only in very severe winters does it get cold enough to overturn the entire water body. This lack of mixing creates a semi-permanent hypolimnion, a region at the bottom of the lake with very low oxygen levels.

After a long breakaway yesterday and today, Warren Barguil very nearly pulled off a win with a sprint to the line in Chambéry, but Rigoberto Uran beat him out by a hair. A sad day for Richie Porte, though, and we hope that he recovers from that absolutely horrific crash down the Mont du Chat.

A rest day for the peloton and for Les Eaux tomorrow, but we’ll be back on Tuesday to see how well the sprinters can recover from these grueling mountains.

  • Vinçon-Leite et al. (1995). Contribution of mathematical modeling to lake ecosystem understanding: Lake Bourget (Savoy, France), Hydrobiologia

One thought on “Stage 9: Nantua to Chambéry

  1. Pingback: Stage 19: Embrun to Salon-de-Provence | Les Eaux du Tour

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