The Bug:

You cannot begin swimming in water while using items.

If the player is in the swimming state and they use an item, they will remain in the swimming state and this is intentional per MC-278028. However, when is a player is not in the swimming state and starts using an item, they cannot enter the swimming state which seems a bit wrong. If using items underwater retains the player's swimming state, they players should be allowed to begin swimming while using items.

Steps to Reproduce:

1. Enter a large area of water and obtain a trident.
2. Begin swimming and begin using the trident and notice how you remain in the swimming state as expected.
3. Stop swimming, begin using the trident once again, and now attempt to enter the swimming state and observe how you can't.

Observed Behavior:

You cannot begin swimming in water while using items.

Expected Behavior:

You would be able to begin swimming in water while using items.