The landscape is cut in height

I have a landscape with a specific height mountain in the center, when I add the WaterBodyOcean to the scene, the mountain is cut on the top.


To show the cutted moutanin I need to disable the option “Affects Landscape”

but, at that moment, the transition between the landscape e the WaterBodyOcean is not already present as aspected.
What could I do to enable the “Affects Landscape” and show the mountain in the right way?