Underwater effects are triggered for swimming player if camera looks vertically up or down
For swimming player (but not underwater) if rotate camera vertically up (or down) then underwater effects will be triggered.
In vanilla MW no such behavior.
#2 Updated by Gijsbert ter Horst 5 months ago
Confirmed on my Debian machine with a build of master commit 58de366c210e5e8a9b375115f6dd1610e8ca363c
While swimming my characters Z-pos is -120.762344
The effect seems to be caused by the camera/head being too close to the water.
The effect is not exactly symmetrical.
When facing straight down it disappears when I elevate my character to Z-pos: -119.578121185302734374999...
Z-pos -119.578121185302734375 is the lowest position where the effect still occurs.
When facing straight up, it disappears when I elevate my character to Z-pos: -119.655857086181640625
#3 Updated by Gijsbert ter Horst 5 months ago
Note: It does not involve looking exactly straight up or down. There's a small circle for which it occurs when swimming normally. The setangle command behaves differently from actually moving the camera, so I could not get exact numbers, but it is approximately when outside the X-angle interval (-77,77)