Swimming is the act of self-propulsion of oneself through water, which can include diving.
When an Assassin or Templar would dive, they could choose to remain underwater in order to hide or evade enemies, up until the point where they needed to catch their breath. This enabled them to use water in a stealthy manner, allowing for the traversal of otherwise restricted areas unnoticed.
Desmond Miles' ancestors Ezio Auditore da Firenze, Edward Kenway, Haytham Kenway, and Ratonhnhaké:ton, also known as Connor, were capable swimmers, able to dive from great heights and hold their breath for several seconds. Ezio's apprentices in Rome were trained to swim, as their initiation ceremony required performing the Leap of Faith into the Tiber river. However, swimming was slower than freerunning, and it was preferable to jump on whatever surface they could find.
Altaïr Ibn-La'Ahad was capable of swimming, but a glitch in the programming of Animus 1.28 caused him to drown upon contact with water, which was corrected in the Animus 2.0 when Desmond began to relive Ezio's memories. Desmond himself could swim, and used to wash in the creek after morning exercises on the Farm.
The pirates of the Golden Age of Piracy dove underwater to find treasure from Caribbean shipwrecks or caverns, after a large armada of Spain's trading vessels sank and scattered a vast amount of wealth to the seabed. Connor's grandfather, the pirate Edward Kenway and his former quartermaster Adéwalé, each possessed a diving bell on their ships, which allowed them to dive for extended periods of time, since they could place their heads in the apparatus whenever they needed additional oxygen.
Edward and Adéwalé were adept at underwater swimming, being able to push themselves from objects and outcroppings to gain a small boost in speed. When swept into a current, they would position themselves to dodge obstacles. However, in order to increase their maneuverability, Edward and Adéwalé were completely unarmed and were forced to dodge or use their fists against hostile animals like sharks.
The Assassin-turned-Templar Shay Cormac was also a capable swimmer, but had to limit his time in the water due to its often extremely low temperatures, which would cause him to slowly freeze. Aveline de Grandpré, a French-African member of the Assassins from New Orleans, Louisiana was a skilled diver. An example of this presented itself when she swam through the flooded caverns beneath Chichen Itza to find the shards of a Prophecy Disk, and could hold her breath for under a minute.
- Before Assassin's Creed IV: Black Flag, civilians, guards and other characters would instantly drown in water, whereas Assassin apprentices would disappear but not be killed. In Black Flag, most of the characters can swim. However, after Assassin's Creed: Rogue, NPCs would drown upon contact with water once more.
- Aveline, Arno Dorian, Jacob and Evie Frye are the only playable ancestors to date who swam using only front crawl, whereas other ancestors also utilized breaststroke.
- In Assassin's Creed: Unity, if Arno falls and dies in feet-deep or very shallow water, e.g. the moats at the Bastille, he would be as if his limp body were floating.