An Old Rod is able to catch common Water-type Pokémon. It is used in a similar way as a Minecraft fishing rod, although when a Pokémon is hooked, a "!" will appear in the chatbox rather than the bob being pulled down, similar to fishing in the Pokémon games.
Goldeen and Magikarp are possible catches regardless of the biome the player is fishing in. Other Pokémon are only possible catches in biomes that they normally spawn in.