When facing water, open the [START] menu using the 'X' button, then go to [ITEMS]. After that, select [KEY ITEMS] and then the [OLD ROD].
Magikarp and to find it use the old rod on water.
if you don't have surf i would use my good rod or super rod not old rod because it only catches magikarp,
Use a super rod.
Use your Old Rod (for a almost guaranteed Magikarp) in any water. Or use your Super Rod in almost any water (I can't remember the specific ponds).
use the super rod in body of waters
Pastoria City and Pokemon League, use super rod
in the safari zone, use the super rod
Canalave City use good rod.
You have to use the Super Rod on Route 226.
use good rod at route 224! ^_^
use good rod at route 222
You can catch them if you use your old rod in water.