Fishing is a great way to catch water-type Pokémon in Brilliant Diamond and Shining Pearl, but you may need some special rods to catch rare Pokémon. You can get the Old Rod at first, but you’ll need to update it soon. You can get the Old Rod by traveling west from the town of Oreburgh to Route 218. There is a man on this route who will give you the Old Rod if you talk to him.
To obtain the Good Rod, players will need to head to Route 209 east of Hearthome City. Players will end up arriving at a place with water and a lot of wooden piers. Talk to a Fisher NPC here to get the Good Rod.
The Super Rod is much harder to come by than the other two. It can only be obtained after defeating the Elite Four. Head northeast of the map and visit the Fight Area and you will find another fisherman. Talking to him will give you the Super Rod.
Fishing rods are actually very useful to increase your variety of options in battles and finish the PokéDex, which you will have to do if you want to pass to the National Dex and all the more secret Pokémon that are hidden throughout the game.