So when the player goes underwater and their head is submerged, they get the usual water visual effect that makes them look like they are viewing the world from underwater. However, sometimes, when the user goes off Minecraft and then goes back on, or even just randomly, this visual effect is replaced by an entirely black screen. I don't know why it happens bit it means you can't go underwater as you can't see anything

 I recently reinstalled Minecraft twice and it still happens, not using texture packs or behaviour packs, and happens on new worlds too.

I would include a screenshot but it's literally a black screen, so...