This is a pretty rational fear, I think. The water is a lot deeper than it appears, at least ten feet; it's much warmer than a hot tub, and I think for most, spending any length of time in it would probably give you heat exhaustion, at the very least. It's also odd how depending on where you're looking, the waters is clear or opaque... it's a strange phenomenon.
Getting into the cave was fussy, but not hard. I'm sure you would have ended up on that first rock just to check it out... for science <3
I once visited the old cruise ship in Florida that is kept as a museum (Queen Mary I think?) and they had an enclosed section around the screws. Big boxed in section and a catwalk hanging 30ft out over the water, which was clear enough to see down into for another 30-40 ft. I actually got vertigo. Clear water just messes with my head in those situations.