I've reported this elsewhere, but might as well do so here too.
If you die while swimming, you will be ressurected still swimming on land. And there will be no way to stand up again, zoning won't do it, terminating won't do it, /quitting won't do it.
The only way out is to slowly swim your way across the land to the nearest lake or other body of water. Once you are swimming in the water, you'll be able to exit it and stand again.