While swimming, you can trick the oxygen bar into thinking you are not swimming by spamming jump button on the surface of the water.

Visual Bug: Sometimes, the player model in the top right corner also shows that you are running, even though you are clearly not.

Code Bug: You can trick the oxygen bar into thinking that you aren't swimming by spamming the button "A" / jump button while swimming on the surface of the water. You will still be able to swim at full speed while not losing any air on the oxygen bar.

 

Footage: Pending Upload