Years ago*, I was snorkeling with a friend far off Keawaula Beach (Yokohama Beach), and felt slightly dizzy, so I announced the problem and immediately swam toward shore.  Don't know what caused it, but I can imagine a tourist wanting to continue snorkeling to get his money's worth during a short vacation.  Being unconscious under water would be double bad.
* "So long ago it seems it was a dream"