I never learned how to swim properly, and I'm 25 now. When I was young, probably 6ish, a friend's mother took my friend and I down to a local river. My friend and I, plus some other kid that I don't remember, went walking out into what we thought was a shallow part. It dropped off near the middle, and I managed to get my foot caught between several rocks. The other two kids helped me to get out, but I was trapped with my head under water for probably a good 30 seconds.
That was probably the longest 30 seconds of my life. Since then, I've taught myself some swimming skills, but I'm still not confident enough to go in a deep end of a pool. After what happened as a kid, I just don't enjoy the water enough to learn.