When you sprint-swim underwater you can't stop
after you stop moving, the character doesnt stop swimming
you stay in swimming mode, but also stay in PLACE, and the height of where you're looking at makes you move up and down IN PLACE
You can only exit swimming mode by jumping out of water

When in creative mode, you can't fly until you exit the swimming mode (which is only possible when you leave water, and that can be a pain in the *** )