How would I be able to make a mesh for an ocean?

[oomer1]

I am trying to build an ocean for my map, but I’m having trouble making the mesh extend beyond the terrain without overlapping the main part of the map, so I can create underground sections.

Here is what I mean:

If I load the mesh in Blender, This is what it looks like:

How would I be able to achieve this? I have very little experience with Blender.

It is really late as I am posting this, so I may not respond immediately.

[oomer1]

I know no one replied, but I figured out how to do this.

I made a union with a tiny hole in it. Then, Imported it as a mesh and made the size large.