Gyarados in Pokemon emerald

Answer 1

In Pokémon Emerald, you can catch a wild Gyarados by fishing for one in Sootopolis City additionally you can catch wild Magikarp in all bodies of water with the Old Rod fishing item and then after catching Magikarp you can raise it until it reaches the level of Level 20 at which point Magikarp will evolve into Gyarados.

Answer 2

Evolve Magikarp. Or Catch it with a super rod around sootopolis.