The new(ish) Flooded Drains area spawns normal "nook" explorables, which is a bit odd, since you are underwater, then climb down a rope to a place with air.
I also found a "scavanger hole" in that area today, and unlike the nooks, I was still underwater (breath countdown etc), but there was no discolouration or haze to indicate it was underwater. It just seemed like a normal, non-water area. This could be fatally confusing for new players.
Absolutely sure the scavenger holes are out of place now.
I went into one just now that despite being "underwater", had nightmare bats flying around!
(https://i.imgur.com/b6yQjhm.png)
Well I was sort of imagining it as sealed hatches leading into deeper air-bubbley chambers, but I guess you're right it doens't make much sense. I removed them.