Nothing happens if the unown you catch can be arranged to spell water.
In HeartGold you can catch Kyogre.
you click on the water with a Pokemon with surf
Use a fishing rod.
Pokethan.
Staryu.
A water stone
Some good water Pokemon include (in their fully evolved form):BlastoiseFeraligatrKingdraGarydosKabutops
The Johto starters, Tododile the Water Pokemon, Chikorita the Grass Pokemon, and Cyndaquil the Fire Pokemon
You need the HM Waterfall and teach it to a water Pokemon
All water pokemon!
You buy it with points at the Pokeathlon Dome.
in the water near cinwood city