Where to find kyoger in Pokemon Emerald?

you can find kyoger in the cave of orgin

After the event between the three Pokemon (Groudon, Kyogre and Rayquaza) go to the weather station. They'll say where the location is for Groudon and Kyogre by saying where there's drought or rain respectably. Go to the route mentioned and look for an area that looks different than the last time you were there. Both are located in underwater caverns and both are level 70. Be prepared for a real tough challenge.