I recognized before...that there is a slight FPS drops underwater but before it went from a stable 60 FPS to around 40 - 50 FPS (while diving).
So that was barely noticeable.
After these hotfixes (v1.1-1221) it randomly drops down to 20 - 30 FPS and 'up' to 40 - 45 FPS. I tried running it on Steam Deck and there seems to be the same issue.
#Underwater FPS drops on PC and Steam Deck
teal latch
static patrol
Having the same issue here on Steam Deck, also on v1.1-1221, no matter the graphics settings. Tried re-entering the diving area (went back up to land, then went diving again), but the issue persists
atomic cairn
Hello everyone! Thank you for bringing this to our attention.
To help us better understand the issue, could you share a video showing the FPS details when you go diving?
You can enable your FPS by:
On Steam, open Steam (top left screen) > Settings > In-Game and make sure Enable the Steam Overlay while in-game is turned on. Chang the In-game FPS counter into “top-right” and enable the In-game FPS counter high contrast.
static patrol
Hello everyone! Thank you for bringing this to our attention.
To help us better...
First clip shows how I went from 60 fps on land to about 20ish underwater. Second clip shows that opening the map underwater gives me high 50s fps, but once I closed the map I was back to 20ish fps
I'm on Steam Deck OLED (512 GB), v1.1-1221
atomic cairn
First clip shows how I went from 60 fps on land to about 20ish underwater. Secon...
That's helpful! Thank you for sending us the videos. I'll relay this to our team for checking. 
atomic cairn
First clip shows how I went from 60 fps on land to about 20ish underwater. Secon...
Hi @static patrol! Our team will also need your save file to investigate this further. Can you please send it to us?
Your save file is most likely stored in the 'compatdata' directory. The filepath is: /home/deck/.local/share/Steam/steamapps/compatdata.
From there, you will see many folders with random numbers. The Coral Island folder should have the code number '1158160'.
Enter that folder, then navigate to the pfx folder, then drive_c folder. Follow this path: Users<username>\AppData\Local\ProjectCoral\Saved\SaveGames to find your save file. It's the 'DailySave_(number).sav' file. Thank you!
atomic cairn
Hi everyone! If you tried to change your tail other than the Arcana Tail, does the FPS drop issue still occur? Thank you!
orchid briar
What is the arcana tail again?
I'm also experiencing this FPS drop, and I want to confirm
orchid briar
Okay, so I changed my merman tail, and the FPS improved substantially
patent coral
Can confirm, also on steam deck. I switched from arcana to shark tail, and it’s a drastic improvement (but now I can’t rebuy the pretty tail? 🥲)
Oh. Just noticed the patch notes for v1.1-1222 includes a fix for this issue. Currently forcing steam to update the game, let’s hope I don’t have to sacrifice the tail 🙂
Edit: yes. It’s much better now
atomic cairn
Hello everyone! Yes, yes. Our team has released the fix for the FPS drop issue when using Arcana Tail.
If you experiencing any SPF drop problem again, kindly send us a video of your detailed in-game activities and also the FPS counter. Thank you!
static patrol
Can confirm, also on steam deck. I switched from arcana to shark tail, and it’s ...
On v1.1-1222 now (on Steam Deck OLED) and yes, the fps has improved for me now too to about high 20s to low 30s fps with the arcana tail. If I go to the tail shop to purchase and use a different tail, my fps jumps back up to close to 60 fps again after using the new tail.
Just like Ap Pa however, I don't see an option to rebuy the arcana tail. Unsure if that's intended (if the arcana tail is meant to be a reward in the future rather than a purchase-able tail), or also a bug