It part of the protesting movement against the megabassine in what protesters call now the “water war”. The objective of this particular protest was to block the port of the city of La Rochelle which is considered by protester to enable the owner of the megabassine to do the business that require such a big use of water. The mouvement has its own french wikipédia article . You can use a translator to learn more about it there.
Same for me.