Concentrate on the cut throughs and the middle. I found the margins to be not the most productive.
Bait, All the usual suspects fit the bill Boilies, maize, tigers, hemp, groats.
Don't go mad with the bait at first. 3-4k of particles and 1-2k of boilies over 24hrs.
be prepared to move if its not happening after 2-3days and bait up other spots in preperation.
if using boilies as hookbaits use 18mm or bigger, hard, or even covered with mesh or shrink tube. The seine contains poison chat (small catfish) that will murder soft baits.
It's a while since I've done any 'Wild' fishing in france. But I'll be getting back in the saddle this year. Its very hard work fishing the rivers but when you get the results you know you deserve it and to me the fish are far more worthy than any from over stocked comercial lakes.
Good luck.