Grassrivers

Grassrivers is Leonida's Everglades, and it is the clearest example of Rockstar building a region around a vehicle rather than the other way round. The airboat is a new class for the series, and this is what it exists for.

A region where your car is the wrong answer

Shallow marsh is the one terrain type where the standard GTA solution — steal a fast car, drive at the objective — stops working. That is unusual and interesting. It forces a different pace: slower, noisier, with much less cover than a city street and far fewer routes than an open highway.

It also changes what a chase means. On a road you outrun pursuit. On water with no walls, you are visible from a long way off and there is nowhere to break line of sight. If the wetlands are used for missions at all, they will not feel like city missions with a boat swapped in.

Hunting, fishing, and why they matter here

Wildlife including alligators has been shown, and hunting and fishing are pitched as things you do in this region specifically. Rockstar has done hunting seriously before — Red Dead Redemption 2 built a full economy around it — so it is reasonable to expect more than a minigame.

That said, nobody outside Rockstar knows whether hunting in GTA 6 feeds an economy, a crafting system, or nothing at all. Reasonable expectation is not confirmation, and the difference matters when people start selling you guides to systems that may not exist.

What is confirmed versus assumed

Confirmed: the wetland region exists, the airboat is a new vehicle class built for it, and wildlife including alligators is present. Assumed: that the marsh is large, that hunting is deep, and that missions are set here. None of the second group has been stated by Rockstar.