Hi Terry, What do you mean by a ‘day fishery’? Do you mean a commercial water that you pay a day ticket or just somewhere to fish that will have other anglers present for comfort & reassurance?
For the latter if you look up your department’s fisheries website by searching on Google using the keywords “Peche 85” it will give you a link to the information page where you can follow the links to Parcourse de Peche (fishing locations) and then to Carpe de Nuit or Carpedrome which are the specific carp fishing locations.
You can find useful information by using “peche carpe vendee” in Google including this list of carp public waters: http://www.powercarp.com/lieux-publics-peche-carpe-departement.php?dep=85
If the Vendee is anything like the areas I fish (Charente / Haute Vienne / Vienne) there will be UK carp anglers bivvied up on waters that produce fish. You can tell the UK anglers as they don’t have their rods set at waist height with tight lines stretching out half way across the lake 😉
You can also find some useful information about private lakes online: http://www.vendee-tourism.co.uk/see-and-do/nature-activities/fishing/