Any water/ocean themed wads you know of?

I'm honestly just curious, because it seems like an original, untapped idea. Plus, I'd be a nice change of pace.

Under a Freezing Sea has a elaborated underwater section

https://www.doomworld.com/idgames/levels/doom2/a-c/aboocean

https://www.doomworld.com/idgames/levels/doom/s-u/undersea

just the first that comes in my mind now

The UAC Ocean Base (Definitive Edition)

Swim With The Whales 

- Water Spirit

- Object 34: Sonar

- Waterlab GZD

- The entire 3rd episode of The Joy of Mapping 5

- Armageddon Invasion 2 MAP12

- Pirate Doom, if that counts

In addition to those already mentioned, the following come to mind:

The Ocean Base (which I reviewed here)

Symocean (features a submarine with a periscope, sort of)

Das Boot (submarine, though all the action takes place within the vessel)

There are plenty of maps with a waterside/harbour theme, including The Waterfront and some maps in Hacx. More in this thread.

Even though it isn't under water, Arctic Research Center A1 (reviewed by me here) has a related theme.

Arcadia Demade

It's a single level that takes place inside a structure that is completely underwater, complete with a new sky to reflect the underwater exterior.

Eden by rdwpa might have more water than the Pacific Ocean so it's worth to check out.

A couple more:

+ Sunlust Map08-10 and Map21

+ Mayhem13 Map 09

+ Port Glacia 

Unconventional examples:

+ Endgame Map07 (It's a techbase with a neat water mechanic)

+ A.L.T Map26 (Look at screenshot below, yes it's green and red waterfalls)

Caverns of Darkness has an all-underwater level.