Q&A for How to Breathe Underwater in Minecraft

Put a nether ward into a brewing stand along with 3 water bottles. After the bottles are brewed, replace the nether ward with a pufferfish. You may also replace the pufferfish with redstone to increase the duration of the potion.

Heart of the sea has a 100% chance of spawning in treasure chests on both Java and Bedrock Editions of Minecraft. This means that as long as you find a treasure map and follow it to the X (which is roughly where the chest is located), you will definitely find one. To find a treasure map, you should check sunken ships or ocean ruins. Alternatively, if you have cheats enabled on your world, just type /locate structure buried_treasure, which will tell you where the buried treasure is.

You can use a door to make an air pocket, but only in Java Edition. In Bedrock Edition, the door will automatically be waterlogged.

No, unfortunately. I don't recommend trying this! You can swim up to the surface to get a breath.