Just because you're a good swimmer, doesn't mean you shouldn't follow all boat safety protocols.
I spent nine months teaching (among other things) a Lake Study class to students from the Chicago area. Part of the class involved taking the students out on this pontoon boat, tooling around the lake for a bit, and doing some water quality tests through the trap door in the boat's floor.
Some students resisted the need for a personal flotation device, citing the hundreds of times they'd gone boating with their families when they weren't forced to wear one. My favorite incident featured the opposite reaction.
These boats were a bit finicky, and on this particular day, there was a crystal clear blue sky. The sun was shining, but it wasn't hot; it was a warm pleasant temperature. It seemed as though everyone in the area were out on the lake with their boats. I started up the pontoon boat with no problems, and handed off a radio to one of the employees scheduled to be on the dock that day, in case of emergencies.
As we pulled away from the dock a bit, I watched as the guy with my radio walked into the boat house and left the radio inside. He hadn't understood that I wanted him to carry it with him until we got back 45 minutes later. Oh well, we were out of earshot now.
In the middle of the lake, I cut the engine and we did our water tests. When I went to start the engine back up again, it wouldn't start. No problem, we had been trained for this. I tried everything. One of the parts of the engine that's supposed to, you know, move just wouldn't budge. It was completely stuck. I had no tools.
But, here's the thing: worst case scenario is we sit on a boat in the middle of a huge gorgeous lake with a pleasantly warm sun beating down on us, and in an hour or so someone will realize we haven't come back yet and come get us. That was the absolute worst possible thing that could happen to us at that moment.
And yet, the students took this opportunity to freak out. They screamed at the top of their lungs repeatedly, "We're gonna die!" There was nothing I could do to console them. They insisted on screaming and waving their arms frantically at every boat that came marginally near us, hoping to be rescued from their predicament of having been stuck on a boat for 15 minutes. Finally, another boat came close enough to hear and towed us to shore.
I was really looking forward to my mini-vacation in the middle of the lake. Sadly, we made it back to the dock before anyone had noticed we were late. I hope those students were happy that they made it to their next class on time with no legitimate excuse to be late for it...