Yes, but "in the water" includes both shallow water near shore and deep water far out in the ocean. The OP is about one. You're talking about the other, which might not even be relevant, so the "anyone knows" condescension is misplaced.

This (coastal area) also happens to be where the vast majority of fish live. This doesn't change the context, but it's something to consider.

What do you mean might not even be relevant?

Is there some hidden reason we should be focusing on deep sea plastics only?

It's not hidden. It's what the OP is about. It's right there in the title - ocean plastic waste, not coastal. Pollution on or near shore is absolutely an important issue, but there are thousands of important issues that are not germane to this conversation.

I'm pretty sure the plastic coastal waste we're talking about it still in the ocean, so I'm a bit confused by the distinction you're making.

Care to explain more?

Mostly in places with no regulation or poor regulation enforcement —at least since the “Don’t mess with Texas” days.

That's still a small amount of trash compared to what gets intentionally dumped in the ocean, plus abandoned commercial-scale fishing equipment.