@Rendeholic....to get rid of the water plane/Sea (or any object that ever has 'Cut' greyed out) , ...rightclick on the Sea and select 'Replace By' (Fit Object)...then from the options of items to replace it with, just select 'sphere'...then the Sea will turn into a sphere...then rightclick on the sphere and select 'Cut'

 

Mary (aka Pixlgirl)