Addon: Infinite Water
Infinite Water removes the normal oxygen limitation while the player is submerged. Drowning damage is blocked, allowing uninterrupted travel through oceans, rivers, flooded caves and underwater structures.
Author: NamanStudios

The addon is useful for building large underwater bases, searching shipwrecks and monuments, collecting marine resources or mining below water without returning to the surface every few seconds.
There are no commands, consumable potions or special equipment. Enable the addon for the world and the protection works automatically.
How to install the add-on
Download the .mcaddon or .mcpack file, open it with Minecraft and wait for the import to finish. Then enable the resource and behavior packs in the world settings. If the add-on requires experiments, turn them on before launching the world.