http://spotthedrowningchild.com/

You should try this. I was a lifeguard for several years, and I think the key is that there are almost always signs a person can’t actually swim. They cling to a flotation device, they stand up to their tip toes in shallow water, they seem visibly uneasy in the deep. They’re the ones who are going to get in trouble, it’s comparatively quite rare for a strong swimmer to suddenly start drowning.

I didn't know what a wave pool is (I've never been to a water park) but they do seem like an awful idea . Wikipedia says they can be hard to lifeguard:

Safety

Wave pools are more difficult to lifeguard than still pools as the moving water (sometimes combined with sun glare) make it difficult to watch all swimmers. Unlike passive pool safety camera systems, computer-automated drowning detection systems do not work in wave pools.[11] There are also safety concerns in regards to water quality, as wave pools are difficult to chlorinate.

In the 1980s, three people died in the original 8-foot-deep (2.4 m) Tidal Wave pool at New Jersey's Action Park, which also kept the lifeguards busy rescuing patrons who overestimated their swimming ability. On the wave pool's opening day, it is said up to 100 people had to be rescued.[12]

https://en.wikipedia.org/wiki/Wave_pool#Safety