If you are on a boat, you really should wear a life jacket regardless of your swimming ability. It sets a good example for people who may not be good swimmers. Besides, if for some crazy reason you end up drowning, it saves a bunch of people searching for your body.
This past weekend, the young men in our ward had a campout, and there were 3 young men that wanted to swim across Ruth Lake in the Uintahs. I didn't think that much about it, but the other leaders said no unless I swam along with them. I wasn't wearing a swimsuit, just shorts. I figured I would just go and swim in my shorts. It's a good thing I did. Two of the three boys started to hyperventilate about 1/2 way across the 100-yard length and I had to talk both of them into calming down and just floating on their back to catch their breath. If I hadn't gone, it would have been big trouble. Once across I told them to get out and walk around the shoreline instead of attempting to swim across.
I had my rescue tube with me on the previous day's swim at Butterfly Lake. But today I didn't expect to swim, so I left it at camp. If I would have had the tube it would have been a much safer experience.
The water temp I estimate was just under 70 degrees.
Thinking back I should have had them go one at a time. I had to juggle two struggling swimmers and thankfully it was such a short distance and I was able to talk them into calming down just enough to keep them out of a panic which I could see was starting to set in. They were able to float on their back and keep swimming elementary backstroke as I reminded them to "Keep your head back, relax your neck, stomach up, and don't panic."
I think the main issue was the elevation. Ruth Lake sits at 10,300 feet which is very high, especially for boys that aren't great swimmers. It was a pretty dumb idea actually, but thankfully it turned out without an incident.