This is a repost of MC-126269 for Bedrock Minecraft
The increased brightness effect given by entering water applies a much brighter view of areas that would be much darker in normal circumstances. Simply pouring water anywhere (ie. cave) will function similar to the levels of night vision.
Video Example
Linked issues
is duplicated by 7
relates to 1
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Does it effect versions with Renderdragon re-enabled?

Affects 1.16.100
Affects 1.16.200.56 Beta

This continues to affect the current full release and the 1.17 betas, and makes it so that you can see clearly in absolutely pitch black areas, both underground and at the ocean floor.

I personally like the higher brightness underwater. It really helps make underwater caves look beautiful. I'd say all underwater vision needs is the texture overlay

The current underwater lighting allows you to see in completely dark caves, with no light source, just by just placing a bucket of water and a trapdoor (as shown in the video example in the bug report). Leaving it as is means Bedrock players will essentially be able to get free night vision in the new caves.

Affects 1.17.10.20

Affects 1.18.0.21.
The most recently attached image is of an underwater cave in complete darkness (light level zero). You can still see clearly without the use of nightvision.

Affects 1.17.41
Affects 1.18.0.24

Affects 1.18.31

Does it affect latest release?

Still affects most current version (Preview 1.19.50.21).
I’ve attached four more images, which detail a view just above the water (where light levels are visible), and just below the water (where the forced night vision makes light levels impossible to discern). .

Affects the 1.19.50 full release, as well as Preview 1.19.60.22.

The bug still affects the most current version, Preview 1.20.30.22.
I’ve removed redundant images for clarity on this issue, as well as added a gif showing the bug in action.
The collage from November 16th shows the light-level visibility to the player when they are not submerged in water, and when they are. I’ve used spectator mode to dip just below the surface, without engaging the “water vision” visual effect.
The new collage (August 21, 2023) shows this same visual bug by viewing water from just above the surface and just below.
The new gif (August 21, 2023) shows the player entering and exiting water in what should be total darkness. The light level is zero, both in and out of the water, but the bug illuminates the area while the player is submerged. This perfectly encapsulates the issue, as in Java edition, the player is not given night-vision simply by being completely under water.

The bug still affects the most current version, Preview 1.21.0.26.

affects the latest 1.21 release

in Java Edition. In the water and in the air, the brightness of the environment is the same, it does not brighten or darken, it does not change brightness depending on the distance from the water, it is the water block that reduces the light of the block's sky, and the visual effect seems to be only a blue filter on the screen and a thick fog in the distance, which can be solved by changing it like Java

This bug is still present in the current preview, 1.21.40.25

Affects current Preview, 1.21.50.24

Affects current Preview, 1.21.50.25
A new observation for this bug is that the time of day seems to affect visibility, even if the player has zero exposure to the sky. To replicate:
1) Create and stand in a player sized box with no light exposure.
2) Fill it with water
3) Toggle time of day between day and night
Inexplicably, it will get brighter and darker within the box.

Affects version 1.21.50.26.

Affects the most recent Preview, 1.21.60.21.

Affects Preview 1.21.60.23.

This bug is still present in preview 1.21.80.25.
As detailed by above, this bug gives an unlisted night-vision effect to the player anytime they are underwater. It is connected to MCPE-84513, which also gives the player night-vision that directly coralates to their vertical height.
Time of day affects the intensity of the night-vision granted, regardless of whether or not the player is underground.
This bug should be considered a parity issue, because water does not at all behave like this in Java Edition.
By the look if it, there doesn't seem to be an attempt to fix this issue. Perhaps it's insignificant or too difficult to fix?