i just used rock smash
It is southeast of Sootopolis and Mossdeep. I recommend travelling there from Mossdeep.
MOSSDEEP CITY
in the city mossdeep
Mossdeep City.
you have to surf from Lincoln .
West from mossdeep city.
Mossdeep City
You have to surf from LILYCOVE city to the right
Mossdeep City is in Ruby, Sapphire, and Emerald.
in mossdeep city steven gives it to you
Mossdeep City
Get to Lilycove City, and once you defeat the Aqua hideout just to the northeast of the city, the wailmer will move, and you can surf east to Mossdeep.