It depends, what waterfall exactly (which location?) ?
They just will show you new areas once you get past them.
Also, special ones: a waterfall precedes Victory Road, another one precedes the Pokemon League. :)
your Pokemon fly off with you in the distance. Then you fall off him/her and fall in to the water. the you beat the game.
This event only happens on the 12th of january. You see dust instead of snow and you can change your date on your ds to make it go back to or go to that date.
I think you are talking about manaphy, you can get it from beating Pokemon Ranger and getting the manaphy egg then transfering it to Pokemon Diamond or Pearl. Or you can go to a manaphy event to get it.
in Pokemon diamond i got waterfall from a girl in sunny shore city ( the girl was on bottom floor north) hope it help:)
January 12
Just head north of sunny shore city go through the victory cave and use water fall and there u are
yes u can get water fall in Pokemon dimond and pearl beat the 8th gym leader and go to the little island (by the pokemart^)talk to the girl she will give u waterfall don't worry the aleat 4 is easy if u have a starter Pokemon (empoleon surf save them)good tip!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Water fall
I think it is the same as Pokemon diamond and pearl you use headbutt on a certain tree and a Pokemon could fall out of a tree
keep training, all legendary Pokemon fall in time
Route 18.
it is water fall and it is in ice fall cave