There is too much fog in the water compared to 1.16.5
edit: I noticed that there is more fog when your render distance is lower. This only happens if my render distance is 8 or less, and if I have my render distance at 2, I can barely see 3 blocks ahead of me
edit: it looks like it has been fixed now.
Please attach a screenshot without Optifine. Also make sure that the settings are exactly the same between the versions.