All I can suggest is that you shout “Shark!”.
Of course it would need to be in Japanese… which as everyone knows is 鮫. Prize of brain of the week to the first person that can give us a voice recording of this (it’s all in the name of research) – the awesome title of Brain of the Week.
Actually I do have another suggestion – get a Dallas pool builder to install your very own pool 
Invite as many friends over as you can and you, too could have your own sea of people.
I guess doing a ‘depth charge’ could get you kicked out of this pool!