Camera effects when the player is underneath a part?

I want to achieve camera effects when the player is under a part such as a water part.
Here’s an example from NDS

I’m not sure how to do this and it would be great if somebody could help me!

im pretty sure thats just gui that activates when you touch the water

I can’t give you an actual example but In one of my games I had a region3 always at the camera and if the region3 was touching water I would change a gui and some lighting settings and then revert them when not, I don’t know if that is efficient and I can’t give an example cuz I don’t actual know how to use them I just threw it together from someone elses code.

If your water is at a certain Y, just detect when the players camera goes below said Y value and add the effect and do the opposite when the camera goes above said Y.