Yes, it’s HaShem who decides, but we have to do our hishtadlus, according to V’nishmartem, and yes, it isn’t rocket science to wear a vest out boating or not to swim where there isn’t a lifeguard.
We need to make water safety – and other types of safety – part of the yeshiva curriculum, starting in yeshiva ketana. I can swim like a fish, but I would never go into the water on a deserted beach at night, not even knee-high, or let any child with me do anything like that. Every neshama counts.