I've done it before, two years ago. Route 19 when Chain Fishing (I failed to get any Shinies lol). My friend is trying to complete his Regional Dexes but he is going to need a politoed. I restarted my game a month ago so I can't give it to him. I'd like to help him out in catching a politoed.
You have a 5% chance of catching it on a Super Rod on Route 19 only.
Source: Bulbapedia, and a couple months back, I decided to catch every Pokemon that has a 5% chance of appearing via fishing in X, cause I got bored.
