A kid at my high school, who was on the swim team, died from swimming underwater. They did informal competitions to see who could swim the furthest underwater. He was practicing that by himself, and overextended himself, passing out underwater. There were other people in the pool but no one noticed until it was too late.
I'm sure that's not the only case. Between the risk of drowning, and the difficulty for a lifeguard to tell between someone holding their breath underwater vs actually drowning, I'm not surprised a lot of pools have "don't hold your breath underwater" signs.
wow, that's terrible. I was a competitive swimmer in my youth, and we did similar competitions from time to time (very rarely). I've never seen or even heard of a swimmer passing out underwater.
A more common drill we would do in practice were called "hypoxic" sets, where we would do one length of the pool breathing every 3 strokes, then the next every 5 strokes, then 7, 9 etc.. until you were going across the whole length (25 meters) without breathing. Not everyone could do it towards the longer distances without breathing, and the coaches would look out for "cheaters", but never once did anyone pass out. Maybe most swimmers, by way of the typical training and exertion in the pool, just don't develop a very good suppression of the "breath signal". I also never remember seeing anyone purposely hyperventilate so that they can stay under water longer.
I'm sure that's not the only case. Between the risk of drowning, and the difficulty for a lifeguard to tell between someone holding their breath underwater vs actually drowning, I'm not surprised a lot of pools have "don't hold your breath underwater" signs.