Scuba diving

Diving returns and it has been given real depth, in both senses. The official Keys screenshot shows a full reef: coral heads, a sea turtle mid-frame and a diver working along it.

The oxygen meter is the important detail

Reporting on the Extended Look describes an oxygen meter replacing the stamina bar while you are under. That is a small interface change that does a lot of work.

In Grand Theft Auto V, swimming underwater was governed by the same stamina bar as sprinting, which made the seabed a timer rather than a place. A dedicated air supply, with equipment that extends it, turns depth into something you plan for. It is the difference between holding your breath and going diving.

What is down there

Reefs with live coral and fish, turtles, and rays. Footage from the Extended Look also included a character swimming among rays, and dolphins appear at the surface elsewhere in the official material.

Rockstar built an enormous amount of animal behaviour for Red Dead Redemption 2 and has clearly carried the appetite forward. Underwater is one of the few environments where wildlife is the entire content, since there is nothing else to do down there.

Why the Keys make it worth building

The real Florida Keys sit alongside the only living coral barrier reef in the continental United States, which is why the diving industry there exists at all. Rockstar putting reefs in the same place is another case of the map borrowing something real rather than inventing it.

There is also an obvious criminal use for a diving system in a game about smuggling by boat, and Rockstar has not commented on that at all.

What is not known

Whether diving equipment is bought, found or given. Whether there is anything on the seabed worth finding, which in previous games meant wrecks and collectibles. Whether either character can dive.