The light transmission through the water, it's cloudiness, is just way to variable for something like this to work constantly, reliably.
Presumably it's essentially clear of suspended particles, most of the time.
Think driving in fog
To clarify: I mean that, generally speaking, the presence of 'cloudy' water would presumably signify that the seafloor was close. In the open ocean, maybe a sea mount is surrounded by essentially a cloud of particles.
Edit: I think your reply made the thread reach maximum depth, so I'll end it here.. I should do more reading on the topic.