Java Edition guides/Update Aquatic

This guide is designed to teach you about all the changes in 1.13. Disclaimer, this guide assumes you are at least somewhat familiar with 1.12.

New
1.13 adds several new mobs to the game, here is a list of the mobs to look out for:

Biome Names
In 1.13 nearly all the biomes are being renamed, here is a list of the new biome names versus the old names:

For more information see the World Generation section in the 1.13 article.

Water
The physics for water has also been changed in 1.13, and the way the player interacts with water has also changed.

Swimming
There is now an actual swimming animation used by the player while underwater, this can be activated by sprinting underwater, this also allows the player to move in any direction they are looking including down. Player that cannot sprint, i.e. are to hungry to sprint, cannot swim. Crouching underwater also allows you to descend at a faster rate.

While swimming players can go through one block gaps similar to when using an elytra.

Item and Experience
Items and experience orbs now float to the surface of water rather than sink, this make dying underwater easier to deal with since all of your items will be waiting for you at the surface. This also allows for easy vertical item transportation.

Bubble Columns
For more detailed information see Bubble Columns.

Magma and Soul Sand now make bubble columns when placed underwater. Magma will naturally generate in ocean ruins and where underwater ravines meet lava, while soul sand does not currently generate naturally in oceans. Players are able to breath while in bubble columns.

Magma will pull things down to the bottom, this includes items, players, mobs, and boats. Soul sand will push all entities to the surface at a very fast rate.

Breath
The breath meter no longer instantly refills when entering air, this means it is no longer possible to refill the air meter with a torch while underwater.

Vision
Water has been given unique colors depending on the biome you are in.

Water is also now clearer, and the longer you are underwater the clearer it becomes.