How do you get waterfall in Pokemon Emerald?

Answer 1

you have to stop kyogre and groudon from fighting...to do that you have to get rayquayza to fly away at the sky pillar... you hacve to beat the sootopolis gym but Wallace or steven will give it to you before but you have to beat the final gym to use it

Answer 2

Look at the gym in Mossdeep city beat the gym leader in Sootopolis City and then talk to Steven in his home town Team Magma should be there beat them and he will give it to you.