How do you get up a waterfall in Pokemon pearl?

To get up a waterfall in Pokémon Pearl, you will need to use the move "Rock Climb." This move can be learned by certain Pokémon, such as Onix, Geodude, and Magcargo, and allows them to climb up waterfalls and other steep surfaces. To use Rock Climb, simply select it as a move and then press A when you are standing in front of a waterfall. Your Pokémon will then begin to climb up, and once they reach the top, they will be able to cross over to the other side. Please note that not all Pokémon can learn Rock Climb, so you will need to make sure that your team includes a Pokémon that has access to this move in order to get up waterfalls.