When you Surf, you will see dark spots in the sea. You can then use Dive, and go underwater.
Use dive.
You can catch it when you use dive.
You get the abilty to use the move Dive from Tate and Liza in Mossdeep and then you can teach your Pokemon to Dive! X3 POKEMON-1001
simpliy the dark spot leading to sootopolis you have to use dive
get a hm called dive attach it to a water type pokemon and go on water and use dive.
Most water type Pokemon like tentacool.
Simply use dive or an escape rope.
get rayquaza
Since dive is not a HM in firered you will have to trade a Pokemon to a friend that has ruby, sapphire or emerald then using that game use the HM Dive to teach the move Dive to that Pokemon trade it back so firered can have that Pokemon again it will still have Dive however you cannot use it to dive underwater.
Dive is not an HM in leafgreen however some Pokemon can learn it on there own, if you want to have a Pokemon with dive have the Pokemon that you want learn dive in ruby or sapphire or emerald then have them trade you it and now you can use dive but not outside of battle because its not an HM.
You have to use Dive in Sootopolis City and look for it under the sea.
no sadly it can only be used in ruby, sapphire and emerald