It shocks me that we use to go to wave pools like these for elementary school trips. They never even asked us if we could swim or not. I was at least a passable swimmer, but even so, it was so crowded that I remember a couple times getting stuck under the water briefly trying to find my way up between all the feet and inner tubes.

Wait

TFA is like 90% a copy of whatever the PDF is on this website. It just prefixes it with a small story

Yeah it's public domain, originally https://mariovittone.com/2010/05/154/

That last line, "children playing in the water make noise. When they get quiet, you get to them and find out why."

fills me with dread.

As a summer lifeguard when I was younger, I agree with the premise - drowning doesn't look it. Each time I encountered it the key was someone simply staring at me - they don't raise their hands or call for help. It even happened once in my own home swimming pool when a pre-teen got in over his head. His parents definitely didn't notice. Except the very first time when I went over to see what the problem was I now extend a cleaning net to them - they grab on very fast and tightly.