Pokémon FireRed and LeafGreen/Route 20

Trainer Challengers

 * Swimmer(Male) Barry
 * 1) Shellder Lv. 31
 * 2) Cloyster Lv. 31


 * Swimmer(Male) Darrin
 * 1) Horsea Lv. 28
 * 2) Horsea Lv. 28
 * 3) Seadra Lv. 28
 * 4) Horsea Lv. 28


 * Swimmer(Female) Shirley
 * 1) Seadra Lv. 30
 * 2) Horsea Lv. 30
 * 3) Seadra Lv. 30

(found by climbing ashore; she's on the other side of the island)
 * Swimmer(Female) Tiffany
 * 1) Seaking Lv. 35

Pokemon Found
Very incomplete list
 * Surfing: Tentacool (probably all)
 * Super Rod: Krabby (really common), Gyarados (uncommon; found a lv. 20 one)