With a fishing rod that you can obtain in Dewford.
your starter pokemon can be a water type and you can trade water type pokemon with your friends in pokemon ruby
in grass, on water and in caves.
most water Pokemon
water!
You should try to catch the Water Pokemon in the water areas of the game.
A water Pokemon probably the water starter Mudkip
Most Water Pokemon can learn surf in Ruby, like tentacool or wingull.
You can find water on almost every route in Pokemon Ruby. Are you looking for a specific body of water? If so, I can't help you unless you ask for a specific body of water.
kyogre. OBVIOUSLY.
In the grass, caves and water
in grass close by water and in in water and while fishing
just surf on the ocean..