The problem is that water doesn't seem to have any affect on the player or other entites. It can still be picked up and put down with a bucket, but cannot be swum in, there are no particles and oxygen bubbles don't show on the hud. Tridents with riptide do not work either. When in water the blur/fog effect is a bright white/blue.

I don't know how to replicate this unfortuneately, which I know would help a lot, but I don't know how this happened in the first place. I did try replicating this on a separate world by repeating everything i thought may have some kind of effect such as all my commands and spawning of entites with the same nbt data. The water was working normally on this world before this point but later when I tried to use a riptide trident, which this map is based around, it didnt work. All my command blocks are disabled and there are no entities in the world besides some (4) armour stands. As you can see in the video there are no mods or etc.