How do you make an ocean?

I'm trying to add an ocean into the GTA4 map, since there are none. Help?

 

Add a water plane from the editor?

 

How do you make a water plane? all I know how to do is add a river, and I don't know how to make that wide enough so it looks like an ocean.

 

in world editor, look at the scene tree, then at the top, click library, then goto the level tab. after that click on the enviroment tab and there is an object called water plane. double click that and it should bring the water plane into the level

 

Thanks