If you can't swim, bring desthly afraid of water is a good survival instinct.

After an incident of near-drowning as a toddler, my parents prioritized swimming lessons in my childhood. I can never remember not being able to swim. However, when I was in the military, there was a survival swimming section where you had to get in a pool with full clothing and a weapon, and swim a length. You were supposed to keep the weapon above water at all time. So you're doing a side-stroke with one arm holding a 7lb weight above water, in long-sleeved shirt and pants (I recall being grateful no boots or socks). Most of us California boys made it; lots of people didn't make it with the rifle the whole way, or tapped out without getting anywhere at all. The point is, near the end, when I was exhausted from fighting the water, and it was starting to get hard to keep my head above water, I felt an unexpected panic rising. I can easily believe that if it had gone on much longer, the panic would have taken over and years of swimming experienced would go out the window, and I'd have ended up thrashing futiliy in the water like the guys who dropped out at the start.

Drowning is a singularly frightening experience.