Hi Paul,
I'm not sure I'd have a so what attitude about falling into Lake Michigan at any time of year! Unless your in a shallow bay. I'm sure somewhere you can look up the average tempurature of that lake, and will find that it ain't warm at any time of year.
Heck, as long as the water is significantly colder than you are, it can zap your energy in a big hurry. I found that out by sailing on Lake of the Woods in mid-August.
The morale, at the least in big water, always wear a shorty!
Fair winds,
Tim