Use a boat or raft to retrieve the ball if it's in sight. If it's a small lake, you could use a paddle or swim towards it.
A lake ball.
in the sea
With a Master Ball.
Yes its recommended though to use a pokeball that makes it easier to catch lake Pokemon like a net ball or lure ball.
Lake of Rage Mahogany City. I suggest using a Pokemon that can use hypnosis and weaken it to yellow. Then use a net ball, ultra ball, or great ball. I just used a net ball.
you go to team aqua's hideout. in a lake out of lilycove.
Azelf is in the cave at lake valor you just have to go in and a dusk ball or an ultra ball after weakening it and just capture it
master ball event
Lake View Cemetery in Jamestown, NY
Poke ball Dive Ball Great Ball Fast Ball Dusk Ball Quick Ball Sport Ball Premier Ball Luxury Ball Level Ball Love Ball Lure Ball Cherish Ball Repeat Ball Ultra Ball Friend Ball Park Ball Net Ball Gs Ball Heal Ball Heavy Ball Safari Ball Nest Ball Moon Ball Pester Ball Timer Ball Master Ball Team Rocket Ball Dream Ball Fantasy Ball Lake Ball
You are allowed five minutes under the lost ball rule
You can only get it from the PokeWalker (Beautiful Beach with 5000+ steps or Blue Lake with 3500+ steps).