Here's a chart for the last 5 years of the Lake Michigan water temps, by month. Converting Celsius to Fahrenheit ('cause I don't think in Celsius), it looks like the average late July temp was about 63 F.
https://coastwatch.glerl.noaa.gov/stati ... ?lk=m&yr=0Now here's a human survivability chart:
http://www.boatsafe.com/nauticalknowhow/hypothermia.htmBut keep in mind that some die within 3 minutes from cold shock, others survive but die after being rescued. In other words, there aren't any guarantees. Being a strong swimmer makes no difference, as hypothermia weakens everyone, and the effects linger long afterwards.
A few examples from my own experience during my misspent youth:
Rafting down the Salmon River in Idaho in early September as a relatively young (I think I was about 32), very healthy, very strong swimmer, one morning I thought I'd show my manliness (!) by swimming across the river and back. I dove in, and by half way across, I could hardly move. I laid onto my back and sculled back to shore, about a couple hundred yards downstream. It took most of the day to recover, and I was still chilled and shivering at dinner.
Boating on Lake Guernsey, northeast of Wheatland, WY, we were returning from an excursion and saw a small cabin sailboat suddenly flip in the gusty winds. We hurried over there to find 2 adults in the water, with the woman screaming that her baby was inside the boat. Being the very healthy, very strong swimmer that I was, now about 35, and with fantasies of being a hero as a trained WSI, I dove in, swam under the capsized boat, and pulled the 3 year old boy out of it to safety. I then stayed in the water as my friend used his boat to tow the sailboat to shore. I took a hot shower in the motorhome, but I remained chilled for the rest of the weekend.
Attending a conference in Reno, we were all recreating one evening at a lodge on Lake Tahoe. As that same very healthy, very strong swimmer, now a little older (I think maybe 38), I commented about the beautiful lake, and that if I had a swimsuit, I could swim out and around the sailboat that was anchored about 50' off shore. Calling my bluff, the barkeep magically produced a swimsuit. So I did it. Tahoe in July is magnificently cold! I made it, but it took everything I had to make it back to shore, and I shivered for the next 3 days, I think.
All joking aside, cold water immersion and the resulting hypothermia is a very serious thing. That's why today I would not fly over Lake Michigan, or any other body of water (except in a seaplane) unless I could be sure of gliding to shore and being rescued almost immediately. But then, I'm no longer the young, very healthy, very strong swimmer that I once was.
Cary