Most of this people already know of these tricks, but I'm putting them together here. If you are a warlock and want to avoid fatigue when going somewhere you shouldn't...follow these steps:
#1 soulstone yourself. After this, log off for 1/2 hour.
#2 sign back on and create a new soulstone. You are now soulsharded and have another one in your bag with no cooldown!
#3 have Hp pots.
#4 make a healthstone.
When you are swimming and the fatigue hits you, keep swimming until the timer runs out. We all know that when the timer runs out you lost a % of your HP per tick. Use your healthstone to get around this. When you finally die, pop your soulstone, and stone yourself again. Depending on your level/talent...by time your fatigue timer runs out..you should be pretty much up to full health. Use your healthstone to get a little more time, and then rez again. Depending on how you do it...you might even be able to get another healthstone in there.
Well, there you have it. Swimspeed would help greatly too, however I am uncertain if the swim pot shares a cooldown with a health pot. That's a choice you'll have to make yourself.