Where do you find wailmer in pokemon sapphire?

Routes 103, 105, 106, 107, 108, 109, 110, 115, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133 & 134, Dewford Town, EverGrande City, Lilycove City, Mossdeep City, Pacifidlog Town, Seafloor Cavern, Shoal Cave, Slateport City (Fish)

you need to have a super rod or use dive.