I tried adding all things that helped water vision like in the latest snapshot (18w08b). Usually adding night vision, water breathing, and respiration 3 helmets gives a whole 100% clear and transparent look underwater. I know that the vision has been improved as a person who started an early game and didn't have these equipment. But it had backfired to the people who does. I hope this wasn't intended.
Works as intended; see: https://minecraft.net/de-de/article/minecraft-snapshot-18w08a