Hydro Cannon (Japanese: ハイドロカノンHydro Cannon) is the strongest Water-type move in existence introduced in Generation III; it can only be learned by a Water type Starter Pokémon. It is really just another version of Hyper Beam.
The foe is hit with a watery blast. The user must rest on the next turn, however.
Jams the others, and misses one turn of appeals.
Earn +3 if the Pokémon that just went hit max Voltage.
In Diamond, Pearl and Platinum, an elderly man, much like the woman of Cape Brink, appears on Route 228 at the Battle Zone, and will teach it to the three fully evolved Water-type starters of the previous generations, as well as Empoleon. He will also require that the Pokémon that is to learn the move has a high happiness rating.
In HeartGold and SoulSilver, the Move Tutor that can teach Hydro Cannon as well as Blast Burn and Frenzy Plant to their corresponding Pokémon can be found in the Move Deleter/Relearner's house in Blackthorn City.
In Black and White the Move Tutor that can teach Hydro Cannon appears in a house on Route 13, and will teach it to the four fully evolved Water-type starters of the previous generations, as well as Samurott. Like in previous generations, this move tutor will require that the Pokémon he teaches the move to has a high happiness rating.