I don't have an answer, just some observations with my GSD. Large family reunion at a rental house with pool. He could care less about the pool when no one was in it. If someone was in it but not making noise, no problem. Put a couple of teenage boys in it and he hovered around the pool but no barking. But when a couple of girls were in the pool laughing and such, he went ballistic barking his head off and running around.
I noticed the same thing with our neighbor's little girl and the pool. As soon as she was in the pool either laughing or crying, he went nuts but when her brothers were in it yelling like no tomorrow, he just watches.
You could try to acclimate the dog to more noise and more people very slowly using treats maybe and eventually he'll realize no one needs a furry lifeguard.
Lynn & Traveler