Ducolamia
SAYYYY WHAT???
If they wanted to do something different they could create a landlocked region that only has rivers and lakes. But I doubt they'd ever do that because so many water Pokemon an only be found in the ocean.
I mean half the region in hoenn was water with plenty of repeating routes of tentacool, magikarp, and other Pokemon. And Alola is basically just a series of islands. I would not be surprised if they went that route. Anything for a nice bit of change.