Surf east of lilycove city.
Mosdeep in emerald, Sapphire and ruby
by surfing!
go to mosdeep city talk to the professor and he will take you to moon
go to Stevens house at mosdeep city i think it was?
Go to Steven's House in Mosdeep City after you beat everyone in the Museum there.
After you defeat the mosdeep city gym and the team aqua (also in mosdeep city but only after you finished the gym) you can get dive from the guy in the house in the south-west of mosdeep
you get it after beating tate and liza mosdeep city gym leaders and after defeating team magma in space center. Go to steven house in mosdeep city he will give you dive.
Mosdeep City Surf there from Lilycove
Its supposed to be a Super Rod. You have to go to a house behind the Space Center in Mosdeep City.
After beating Mosdeep City Gym.
In Pokémon Ruby Sapphire and Emerald, your journey takes you to Soontololis City. To get there you need to use surf and then dive near Mosdeep City.
Go to the top-left corner of Mosdeep city and go inside the house. There's Steven, who will notice you and give it to you