Train a mudkip to level 36.
The best water Pokemon in Pokemon emerald I believe is Kyogre. kyogre is probably the stongest but i prefer a swampert if you don't like legenderies
Kyogre
Swampert or Wailord.
Level 36.
My Pokemon party is Charizard, Lapras, Dragonite, Aerodactyl, Snorlax, and Kingdra for the Leafgreen version. =)
Swampert's ultimate moves are endeavor, earthquake, hammer arm, and mud bomb
Sceptile is way better than Breloom. Swampert is better than Sharpedo, Swampert is also a Ground type.
Endeavor is a move that can be learned by certain pokemon like Swampert and so on.
CUZ ITS AN HM YA Cookoo
sceptile or a blaizeiken or a swampert
metagross salamence flygon blaziken swampert sceptile
Swampert is the evolvesion of mudkip which is one of the three pokemon you can pick to start out with in the beginning of the game therefore you cannot get him unless you pick mudkip at the beginning of the game