I've never free-swam, but when I was a kid (up to early teens, maybe 14?) I had swimming lessons. I was always told the lessons of the waterways, which I vaguely remember now, but one of them was kick off your shoes because they will kill you. We had to recite those back at the start and end of the lessons, what to do if you fell in. Kick off your shoes because they will kill you.

Only lesson I remember, funnily enough.