X100 fish icon?

This sounds ridiculous but,

I have this fish icon on my LCD right above the battery status icon. It's not described in the manual and I don't really know when it started to appear. It's an image of a fish blowing bubbles under a wavy sea, honest.

I'm pretty sure the X100 doesn't have an underwater option, and I'm wondering what the camera is trying to tell me.

Does anyone else see what I'm seeing?

Gary