speak to your local EHO's especially so noting that a 16 year old is not an adult and an child/minor should not be left alone in many situations especially where they may have to deal with 18/19 year old's - I assume that this is a privately run establishment?

What's the pools risk assessment like? Bet you it does not say that the pool should be left to an untrained apprentice!

16? Lifeguards are often young but, yes, untrained apprentices are not for putting in charge! Whether they should be trained as a lifeguard is entirely dependent on the pool risk assessment - see HSG179 for some further clarification of when trained lifeguards should be necessary. Regardless, some level of first aid and alarm raising training etc. is nearly always the minimum. That aside, pools tend to be dosed with chlorine which needs regular checking/adjusting. Pool dosing plant comes in a variety of sorts but does often have all the constituent parts of a bomb. Just saying.... I mean...actually, the more you begin to look at this the more it quickly becomes apparent this situation is unlikely to be even remotely acceptable....even should they have a bit of paper claiming to be a young persons risk assessment.