I just returned from Lake Superior (Wawa, Ontario) and have to say that while I did pack water, it's one thing that I wouldn't be overly concerned about. Compared to where I usually boat, Lake Superior water is pristine... at least once you get a little ways out
And yeah, that water is cold. However the harden local kayakers considered me over dressed in my dry suit. I didn't care. If for some reason I had to spend some time in that water I would sure be glad I was wearing one.
Hope to return next year.