Cycling from Bordeaux Vineyards to the Atlantic Coast/ Cap Ferret/ Bassin d’Arcachon

A phenomenon which is reflected in the sand and on the collectors of the oyster farms is the red, rusty colour.

In the land of Gascony soil consists of an iron oxide interspersed with sandstone. The water seeping into the groundwater is heavily saturated with dissolved iron, causing visible traces of red and rust on the banks and collectors.