Pokémon Gold and Silver/Fast Ship S.S Aqua

After you have won the league, the credits will roll, then you will be back in New Bark Town. Whenever you move, you will be called by Professor Elm, he wants you to go to his lab, go there and he will give you the S.S.Ticket, now go to Olivine city to catch the ferry "Fast Ship S.S Aqua".