Things You'll Need
Instructions
Catch a Horsea. Horsea can be found by fishing with the Super Rod on Route 132, Route 133 and Route 134 of the Hoenn Region.
Put the Horsea in your party and use it in battle to increase its experience. Getting enough EXP, or experience points, will cause a Pokemon to increase one level.
Raise it to level 32, and it will evolve into Seadra.
Trade with another player to obtain a Seadra if you prefer not to capture Horsea, or are having a difficult time encountering one. In Emerald, your chances of encountering Horsea in battle are only 15 percent every time you fish with the Super Rod.