From Fuchsia City, you can go south to the watery Route 19, where you can battle Swimmers and catch Water-type pokémon.

Explore Route 19

You can optionally visit Route 19 after you learn Sea Skim in Fuchsia City. Route 19 leads to the Seafoam Islands, where you can catch a rare pokémon.

Go south from the Fuchsia City Pokémon Center to reach the route. Jump down the ledge on the left to reach a Full Heal.

Go south down the next ledge and you can battle Swimmer Richard, who has a level 38 Starmie. You get 760 Pokédollars and 3 Poké Balls for winning.

Go east and you can battle Swimmer Reece, who has a level 38 Dratini. You get 760 Pokédollars and 3 Poké Balls for winning.

Go south and get in the water (talk to the Surfer in the Fuchsia City Safari Zone if you haven't learned Sea Skim yet). Go south and you can battle Beauty Alice, who has a level 41 Golduck and a level 41 Cloyster. You get 820 Pokédollars and 3 Poké Balls for winning.

Go southwest and you can battle Swimmer Axle, who has a level 42 Poliwhirl. You get 840 Pokédollars and 3 Poké Balls for winning.

Go southeast and you can battle Swimmer David, who has a level 42 Seel, a level 42 Seadra, and another level 42 Seel. You get 840 Pokédollars and 3 Poké Balls for winning.

To the southwest, there are two Beauties. The northern one is Beauty Connie, who has a level 41 Vaporeon. You get 820 Pokédollars and 3 Poké Balls for winning.

Southeast of Connie, you can battle Beauty Anya, who has a level 41 Seel and a level 41 Seaking. You get 820 Pokédollars and 3 Poké Balls for winning.

Go west to reach Route 20.