Swimming is a basic move used by Kirby and other playable characters, allowing them to travel underwater. Swimming has taken on various forms and functions throughout the Kirby series, with the main distinction from above-water travel being the inability to use most regular techniques and moves.
The mechanics of swimming have changed several times over the course of the series history. Commonalities include having the characters able to move about freely, using a limited move-set or the Water Gun to attack, and having scuba gear on while underwater. The main limitation comes from Kirby's inability to Inhale unaided while underwater (though one exception exists). Swimming characters are not at risk of drowning (again, with one exception), and can remain underwater indefinitely. Some enemies are capable of surviving in water, but most will immediately drown and burst upon contact with it.
Kirby first had to traverse bodies of water in Kirby's Dream Land. In this title, the only action Kirby can perform in the water is his jump, and jumping repeatedly is how he swims. As such, he has no defensive abilities in the water whatsoever.
Kirby's Adventure was the first game which gave Kirby the Water Gun, in addition to being able to use some abilities like Sword and Hammer underwater. This title also gave him rudimentary swimming ability, though he can still rapidly approach the water's surface by jumping repeatedly.
Kirby Super Star was the first game in the series to give Kirby a scuba mask whenever he enters water, appearing on his face whenever he takes a plunge. While Kirby is still mainly limited to a few options while swimming, his Helpers can perform their usual retinue of actions while underwater (including Burning Leo's Fire breath).
In Kirby 64: The Crystal Shards, Kirby is able to Inhale while underwater, being the only game in the series where he can do this without the help of Kine. As such, he has largely the same moves underwater as on land, though much slower-paced.
In Kirby's Epic Yarn (and Kirby's Extra Epic Yarn), Kirby and Prince Fluff transform into a Submarine form automatically whenever they enter water. While in this form, they propel themselves by means of a rotor in the back, controlled by the player repeatedly tapping the 2 button. They cannot move unless this is being done.
Kirby Mass Attack is the only game in the series where it is possible for Kirby to drown, as he is given an air meter with a capacity dependent on the number of Kirbys together. Air can be replenished by catching air bubbles, and if it runs out, the Kirbys all perish.
Kirby's Return to Dream Land changed swimming in many fundamental ways. While underwater, Kirby and his friends are restricted to four-directional movements and will slowly drift to the bottom of holding still. While on the surface of water, Kirby and his friends gain an inner tube and can paddle left or right, or jump out. Kirby: Triple Deluxe adds two different methods of movement underwater atop Return to Dream Land's base mechanics. Simply holding a direction lets Kirby swim at a modest pace while pressing the A button causes him to perform a hard stroke to pick up speed. Kirby Star Allies adds further to this mechanic by allowing Kirby and his friends to swim and use the Water Gun diagonally.