Where to find Horsea in HeartGold & SoulSilver

Good Rod: Seafoam Islands (10%), Whirl Islands (10%)
Super Rod: Seafoam Islands (30%), Whirl Islands (30%)
Surf: Whirl Islands (90%), Seafoam Islands (30%)

• Seafoam Islands (B4F) — Good Rod, Super Rod, Surf
• Whirl Islands (1F, B2F) — Good Rod, Super Rod, Surf

Horsea in every game · Pokémon HeartGold & SoulSilver interactive map (Johto & Kanto)