The biennial Semaine du Golfe du Morbihan festival of boats (and food, wine and lots of other good things!). See the following forum post and web site for more details:

http://www.swallowyachtsassociation.org/smf/index.php/topic,995.0.html

http://www.semainedugolfe.com/Home-1074-0-0-0.html