Last time I went to a beach, it was during southern winter (tropical climate, so temps never dropped under 20ºC). The only thing that kept me from going further out swimming was the amount of jellyfish being carried by the current.

It's not really about what you can see and clarity, but it's true that clearer water is much more psychologically inviting.

We'll bring a smooth granite pebble out with us, while waiting for the swell, drop it down and take turns bringing it back up. We've had dolphins join us in the game once before.

But definitely I don't feel the appeal of diving down and doing that when the sky or water is dark and unclear. It's less inviting.