In Pokémon Scarlet and Violet, you explore the Paldea region, a vast island with different biomes and environments. As an island, there is a lot of water, including the ocean, rivers, and lakes. With all this water to explore, you will need to be able to surf it, which may leave you wondering how to swim or surf in Pokémon Scarlet and Violet.
To swim and surf in Pokémon Scarlet and Violet, you must first progress through the story, namely the Titan and Herba Mystica path, to unlock this ability. Once you have done so, you can simply walk into the water, and you will automatically begin surfing.
How to unlock Swim/Surf in Pokémon Scarlet and Violet
To swim and surf in Pokémon Scarlet and Violet, you must have Koraidon and Miraidon learn how to do so. This is done by defeating the Open Sky Titan, Bombirdier. This Titan is level 19 and has the Flying and Dark-type. You will want to bring a strong Electric or Rock-type Pokémon to defeat this Titan.
You can find the Open Sky Titan Bombirdier in the upper southwest corner of Paldea. This will likely be the first or second Titan Pokémon you encounter, so be prepared to take it out if you want to learn how to surf or swim. Once you defeat it, the waters of Paldea will be available to catch Pokémon.
For more information on Pokémon Scarlet and Violet Best Gym Order (Easiest Route) and Which direction to go first in Pokémon Scarlet & Violet on Pro Game Guides.