My brother was a lifeguard for a few summers too. He was up in the Sierras in a BSA stream 'pool' and the training was much the same. He remembers a time when a little kid, as part of the initial swim eval everyone has to take, jumped off the end of the makeshift dock. He said the kid just sank like a stone. No bubbles, no struggle, nada. The very cold water just shocked the boy so bad he went right to the bottom. Mind you that about 30 or so people are now trying to do the same swim test and the water can be chaotic. Luckily my brother was trained for this. He saw that the kid didn't bubble, 'ok, fine, he's gonna push off the bottom'. He then saw that the kid didn't bend his legs when he got to the bottom, 'ok, sometimes they like the real cold water and just like to lounge at the bottom for a sec. He's got 1 mississippi, 2 mississippi, 3, annnnnnnnnnd now we have a problem'. My brother jumped into the stream and just yanked the kid. This boy was still very awake but petrified and shocked by the water's cold. He gasped for air, and was not cleared then for swim eval that week.
My brother also had some stories about the stream aspect of the pool, and that sometimes fishing hooks would wash downstream and the boys would step on them. He told me he never heard so bad a scream and fight as when a 11 year old stepped on one and had to have 3 grown men hold him down to take the barb out. If you don't know, for barbed hooks, you have continue to push the barb through the wound, a very unpleasant experience. The boy tried to run from the fear, and his scoutmasters had to endure punches and yells from the boy for his own good. Sends chills down my spine and I wasn't there like my brother was having to hold the kid.