Going under waterlogged stairs gives underwater effect

When going under a waterlogged stair block, the game will give you the underwater fog effect you get when you typically go under water.

 

You can recreate this by waterlogging any stair block with a water bucket, then going under it. (Example below)

Note: You do have to be touching the underside of the stair for this to happen. Simply being under it has no effect.

Here is the effect in action: