I came across an interesting article that was published by the local tourist guide Marie Hallier (Teleprotour Private tours) on her Fa...

Why is the Garonne river brown? Here is the explanation!

I came across an interesting article that was published by the local tourist guide Marie Hallier (Teleprotour Private tours) on her Facebook page. Marie kindly agreed to let Invisible Bordeaux reuse the article, which explains why the waters of the river Garonne are brown in response to one of the recurring questions Marie gets asked: why does the Garonne look so dirty?

Marie says: “To begin with, it is wrong to say the water is dirty, the exact term is “turbid” (cloudy or opaque). OK, it’s not easy to slip that word into conversations but it could prove useful the next time you play Scrabble! Other ways of describing the colour in French include “limoneuse” (loamy), “blonde” or even “café au lait” (milky coffee)…

And don’t listen to what your fellow passenger on the tram is saying. No, the Garonne has not suddenly turned brown because it rained in the Pyrenees last Saturday! The river is actually brown more or less 365 days per year!

The colour is the end-result of a natural phenomenon. To keep things simple, the fresh water (that flows in the Garonne from its source) is laden with sediment (mainly clay from the river bed). With the effect of the oceanic tides, the river comes up against an incoming current made of salty seawater.

In chemical terms, the salty water is heavier than the fresh water, resulting in a kind of undercurrent amplified by the riverbanks and which brings the sediment to the surface. This is referred to poetically in French as “les floculats” (microscopic flakes that form when particles coagulate) and this reaction is what gives the Garonne its lovely brown colour.

Further upstream, at the point where the tidal effect subsides (more or less around Castets-en-Dorthe), the water becomes distinctly clearer. The presence of salty water stops much further downstream, around Bec d’Ambès.

Sometimes, deposits of sediment have been known to latch on to bits of vegetation; this phenomenon is what gave birth to the islands in the Gironde Estuary!

And, it is interesting to note that the Garonne is ranked as one of the cleanest rivers in Europe! So now you know!”

> If you want to know more about the inner workings of the Garonne and the Gironde Estuary, Marie Hallier provides guided tours all year round. Further information available on her website: www.bordeauxcognactourguide.com or via her Facebook page
> All photos and illustrations © Marie Hallier/www.bordeauxcognactourguide.com
> Original version of this article available here
> Ce dossier est également disponible en français !


  1. Surely the tide from the Atlantic doesn't reach Les Eyzies? Here and further upstream the Vezere is also "brun". Maybe it's the same clay sediment?

  2. The real question is : Why is the so much erosion going on in the catchment of this river? Erosion means that valuable furtile soil is being lost. That is something to worry about. It means that the soil gradually will sustain less agriculture.
    Has this massive erosion always been the case? Or must we seek the cause in modern day land use? Erosion happens when soil is loose. Normally plants hold the soil with their roots. But look at pictures of vineyards in the Medoc area. There is no undergrowth!

  3. The soil in between the grapevines is barren. That is not the normal state of soil. Normally all sorts of plants will grow when given the opportunity. Why is the soil in between the vines bare? The most likely explanation is that herbicides are being used.
    Probably the vintners think it is a good idea to kill all the plants in between the grapevines. However they do not realise that this manner of agriculture is killing the chicken with the golden eggs.

  4. Is it just the Garonne River that is brown? Seems to me that the turbidity occurs in the estuary as well as both the Garonne and Dordogne (as far upstream as they are impacted by the tides).

    1. Absolutely, the title of the piece and opening angle is focused on Bordeaux, where people are surprised to see how brown the river is as it flows through the city, but this definitely applies to the Estuary and to the Dordogne's home straight.