Swim

Swimming is an inherent ability of all player characters, and some mobs, which allows one to travel in and under water. Swimming is slower than running, but faster than walking.

When your character is in the water, press the sit key will dive deeper, while pressing the jump key will surface. You can hold the left mouse button to look around. You can hold the right mouse button and then move your mouse up and down to change your swim direction. Moving your character forward or backwards will then make them swim in the direction you have chosen. As a ghost or while water-walking, pressing both mouse buttons and angling the camera downward will allow your ghost to swim.

When underwater, a character begins to run out of breath and may drown. Resurfacing will allow the breath bar to slowly refill. Some underwater places have 'pockets of surfacing air' visualized as underwater air bubbles coming from cracks in the crust or barnacle-like models - you can stay there and fill your breath bar. These pockets are usually places in places related to some underwater quest. Deeper waters (such as around the continents) will fatigue characters, whether they are above or below the surface. When either the breath bar or fatigue bar expires, characters begin to take damage. Both drown and fatigue damage can be healed, allowing the character to go on for a little longer.

Ghosts do not have to breath underwater, but are still affected by fatigue and can be killed a second time.

Methods to breath longer underwater:

 * Several items, including Hydrocane, Mastercraft Kalu'ak Fishing Pole, Deepdive Helmet and Band of Icy Depths allow underwater breathing while equipped.
 * Alchemists can brew Elixir of Water Breathing and Elixir of Greater Water Breathing.
 * Both Shaman and Warlocks have a castable Water Breathing buff.
 * Often, underwater quests will provide a summoned item that will provide underwater breathing.
 * Certain quest rewards, such as Nagrand Cherry, allow short underwater breathing buffs.
 * Druids in their Aquatic Form can breathe underwater. Switching to Aquatic Form after an underwater fight is a convenient way to take a breath before the next fight.
 * Undead players can breathe underwater for 233% longer than normal players due to their Underwater Breathing racial trait.

Methods to bypass the need for swimming:

 * Shamans (at level 28 Water Walking), priests (at level 34 Levitate) and death knights (Path of Frost at level 61) get spells that allow them (and possibly nearby party/raid members) to walk across the water surface — however, taking damage breaks the spell.
 * While in ghost form all characters can intrinsically water-walk. If you want to dive into the water while walking over it, tilt your camera to start pointing down into the water and 'go down'. To step onto the surface of the water while submerged and having cast the spell, hold the jump button. Characters can jump to get back on top of the water, however mounted characters cannot jump high enough, and will fall through.
 * In Outland and Northrend, characters can fly over water with flying mounts. Unlike ground mounts, flying mounts cannot be mounted while in water.

Additional notes

 * Swim speed, unaffected by anything, is just a bit over two-thirds the speed of running.
 * Ground mounts are able to swim, although they travel no faster than an unmounted player. Entering water while on a flying mount will dismount the player.
 * You can escape combat from some mobs if they can't swim; for example, a wolf.
 * You can escape combat from some swimming mobs because they can't leave the water; for example, a threshadon.
 * In the event of an encounter where you do use the transition between land and sea to break a fight, the mob in question will evade but remain in combat with you. It should, in most cases, reset within a few seconds.
 * Some amphibious mobs can pursue from land into the water and swim after you or from water to land and run after you. For example, a murloc.