10km Marathon Swim

10km Marathon Swim is an event that appears exclusively in the Nintendo 3DS version of Mario & Sonic at the London 2012 Olympic Games. The game focuses on collecting drinks as opposed to finishing first like in the real life version of the event, using an elimination process to decide the winner. The character set for this event is Challengers, meaning that Yoshi, Shadow, Bowser Jr., and Silver are playable.

Gameplay
The aim of the game is to be the one who reaches the finish by obtaining a drink every round. Every 30 minutes in the race, an empty heart icon will indicate that the player has little remaining stamina, and the swimmers will approach a series of panels, consisting of red and orange ones which boost the player forwards, similarly to Dash Panels, and green and blue ones which push the player sideways. The player must use to navigate through the panels to the Fishin' Lakitus at the end holding drinks, where there will always be one less than the number of remaining swimmers. The player must tilt the system upwards to be able to see the panels ahead of them and the position of the Lakitus, but this will cause them to slow down and tread water. Once a swimmer collects a drink, they will drink it and swim faster to the next section, however if they fail to do so they will be forced to retire. If two or more swimmers fail to obtain a drink they will both be forced to retire. At the end of the event, the winning character will swim up to the boards at the end of the event and jump up to hit it, although Yoshi uses his tongue to hit the board instead of one of his hands. In the story mode version of the event, as the player only ever competes against one other character, there is only one round and one drink, similar to the final round of the regular event.

Controls
Hold the system horizontally! 1) Move sideways: Move the Circle Pad left/right. 2) Look forward: Tilt system toward you. Swim over the panels to speed up!

Medley Match
In Medley Match mode, 10km Marathon Swim appears as the second event of both the Strategy Master Medley and the Adapt to Survive Medley.

Story Mode
In the story mode, 10km Marathon Swim appears as the third challenge of Challengers Episode 1, The Blocked Bridge, in which Yoshi must beat an imposter of Silver. It also appears as part of challenge one in Challengers Episode 3 Enter Bowser?! alongside Triple Jump and 3000m Steeplechase, in which Yoshi must beat Bowser Jr., and as challenge 4 in Challengers Bonus 2, Junior, Super Hero?, in which Bowser Jr. must beat Silver.