This is an older issue, previously tracked in MC-1531 and MC-68129.
The bug
Smooth lighting doesn't work on the water surface. Simple as that.
Screenshot
[media]Smooth lighting is at maximum in this screenshot.
Note
@unknown is aware of this issue: https://twitter.com/Xilefian/status/1399412383710318592
Linked issues
is duplicated by 8
Attachments
Comments 24
So that the bug can be tracked. Even if they know it now, if they don't plan to fix it, they might forget. So it's still good to have it in a data base.
Why did you report the bug here if you know the developers are aware of the issue?