Having trouble with an underwater border?

[teethcollection]

title is a bit unclear, apologies!

i'm making a fantasy map where one kingdom is entirely submerged underwater, like an atlantis situation, and i'm worried the way i have it demarcated now is not reading correctly. currently, i have the zone colored in with flat color diagonal lines that are a different, distinct blue than the water color.

is the answer here a key? or perhaps the lines should be a color other than blue? dotted line? i'm at a loss here. any help appreciated! thanks!

[Greason Wolfe]

You should probably attach an image here. It is difficult for anyone to offer advice/suggestions without being able to see what you have done and what your concerns about the project are.