This is gonna be vague, but I'm trying as best I can:
- it's at least 360/PS3 era or newer, I don't know if it was on either of those. I played it on PC a few years back. Maybe 5ish or so.
- open world 3d: don't recall if it was first or third person
- there's an island you can get to, and all I remember is that it took some doing to get there, but I don't remember if you swam or what.
- there are boats at a dock but I think they were broken
- there was either a lighthouse or some kind of storage shacks, possibly both
- if you were looking back toward the main map, there was a boat at this island on the coast to your left and I think it was possible to get on top of it. It may have been partially submerged and maybe yellow?
- tall grass on this island
- maybe monsters? maybe zombies
- zero clue about your character or any gameplay mechanics, I just remember finally getting to this island and needing to return at least twice, but I don't remember for what. Maybe collecting materials
My brain is saying it's Dead Island 1, but you don't swim to any islands in Dead Island that I can recall, in any of the areas. If this fuzzy ass memory is enough to pin it down, I thank you much.
[edit - it doesn't jive with some of the stuff I'm saying here, but it might be spectacle island in Fallout 4? I'd hate to reinstall it just to see, but I might]