In the anime, Ash's Squirtle was a wild Pokémon he captured in episode 1 of the series.
Here's how you can find Squirtle in the games:
* Pokemon Red, Blue, and Yellow: Squirtle is one of the three starter Pokémon you can choose from at the beginning of the game.
* Pokemon Gold, Silver, and Crystal: You can find Squirtle in the Lake of Rage after defeating the Elite Four.
* Pokemon Ruby, Sapphire, and Emerald: You can find Squirtle in the Seafloor Cavern after defeating the Elite Four.
* Pokemon Diamond, Pearl, and Platinum: Squirtle can be found on Route 217 after defeating the Elite Four.
* Pokemon Black and White: You can find Squirtle at the Dreamyard after defeating the Elite Four.
* Pokemon X and Y: Squirtle is available at the Friend Safari.
* Pokemon Omega Ruby and Alpha Sapphire: You can find Squirtle in the Seafloor Cavern after defeating the Elite Four.
* Pokemon Sun and Moon: Squirtle can be found in the Battle Tree.
* Pokemon Ultra Sun and Ultra Moon: You can find Squirtle in the Battle Tree.
* Pokemon Sword and Shield: Squirtle is available in the Lake of Outrage after defeating the Elite Four.
* Pokemon Brilliant Diamond and Shining Pearl: You can find Squirtle in the Lake of Rage after defeating the Elite Four.
* Pokemon Legends: Arceus: Squirtle is a rare encounter found in the Crimson Mirelands.
* Pokemon Scarlet and Violet: Squirtle is available in the Treasure Hunt Event (limited time).
Let me know if you'd like to know more about finding Squirtle in a specific game!