Swimming is tough for me. I don't float. Something about body density or whatever, but I genuinely don't float. Not even in saltwater.
So if I'm in the water, I have to constantly be moving, treading water or attempting to swim, to stay on top of it. It tires a person out pretty quickly.
I know how to swim, and I can swim some laps when I want, and I can swim well enough to get to the edge of the lake if my boat goes down in the middle, but I'll never be a triathlete, that's for sure.