Here is a photo by Joho Salo of Rauma, Finland. It shows how some people [namely light weight, strong, and expert teen-aged windsurfers from Poland] can sail in almost no wind. They are on sleds with jumping skis using top quality sails. Now that the maximum sail size for WISSA competition has been raised from 7.5 meters to 9.5 meters, we can go in even LESS wind :-)
Notice that the shore is not visible. That is because Lac saint Jean is so big that you can sail away and lose sight of shore. The snow conditions at WISSA 2010 were perfect. The brief period of light winds during the event were not normal. Regular winds from the west in the 30- 50 kph range came right back as soon as the event was over.