Deaths on Bear Lake
 

http://www.deseretnews.com/article/8...-capsizes.html

They had lifejackets. Illustrates the danger of cold water. Sad deal.

One of the rules of thumb I have heard is to never go out windsurfing when the temperature of the air + water <100. And that's with a wetsuit or a drysuit.

Obviously in a boat you are not expecting to spend a lot of time in the water, or be exhausted like you might be windsurfing. But you never know. Weather can turn on you real quick.