The bug
When only wearing a turtle helmet there are no particles for the water breathing at all, not even ambient ones. However, if the player has a different, ambient effect, for example from a beacon, then non-ambient particles are shown.
Related issues
Comments


The turtle helmet effect is ambient, on its own. The beacon effect is ambient, on its own. Put together, they become obtrusive.

Please do not mark unreleased versions as affected.
You don't have access to them yet.

Confirmed for all snapshots for 1.14 (as of 18w47a)

Still an issue in 1.14.2 pre-4 for me.
[edit] Beacon particles, anyway. I have not ever put on a turtle helmet so I can't speak to that.

In 20w11a I don't seem to be getting turtle helmet particles regardless if im with a beacon or not, but I do get beacon particles regardless if I have a turtle helmet or not

In 20w12a
Apparently affects ambient effects in general. The effect given by the turtle helmet should probably be ambient, but apparently isn't?