HM 03 Surf location in Pokemon Emerald. It will be obtained automatically by Wally's dad after beating the 5th gym leader in Petalburg. In ruby/sapphire you will need to go into the house beside the gym and talk to him after beating the gym.

Where do I find surf in Emerald?

go get the 5 badge and go to the gym of 5 bade and beside it there was a house. Go inside the house and find wally's dad and he will give you HM2 thats the surf.

Where do I go after I get surf in Emerald?

Right after you get surf from Wally's father, teach it to one of your Pokemon and go to route 118. Surf across the water. Hope I helped!