when you get HM surf just get in the water and there's only water pokemon.
You can find them by surfing and fishing.
GROUND
all of them
I believe it is all water types and some others like my snorlax, Chow, can learn surf.
in gold there are lots of different types also the legendary pokemon moltres plus trainer blue
In the water
Water type Pokemon are weak to electric type Pokemon.
Electric types and Grass types.
Fire Pokemon are weak against water types, rock types and ground types.
Other bodies of water and by the water you can get a wooper
Get a fishing rod and fish for one.
I personally like water-psychic Pokemon like any evolution of Polywrath (I think that's its name)