I don't remember how old I was, but I distinctly remember an occurrence at one of my first swim lessons. It was a group class, and we were all hanging on a rope taking turns swimming to the instructor a few feet away. I thought I heard my name called, so I tried to push off the rope to swim to them. Since it was a floating rope, I didn't get the momentum I was expecting, so before I knew it I was frantically trying to get to the rope, or the wall, or the instructor, or ANYthing I could grab onto. After what seemed like hours (but I'm sure was a few seconds) the lifeguard hopped in and grabbed me. It's been at least 20 years, and I'll never ever forget the panic - and to think it happened in the middle of a swim class with an instructor not 10 feet away.
My dad always told me when we went on vacation to the beach to "respect the ocean", and if I ever have kids I will for sure expand that message to "respect the water" and pass it along - whether it's the atlantic or a kiddie pool.