How can I mask the ocean?

As in the figure(from online),how to mask the offshore, and only save the open ocean?

[John D'Errico]

Please don't ask the same question just to try to get more attention to your problem.

[Image Analyst]

This seems to be the only question that shows up now, despite the popup saying he asked 2 questions. So, which colors do you consider to be "offshore"? I'm seeing quite a few colors offshore (right next to the black land masses) - white, blue, green, yellow. So which color(s) do you want?

Please give a desired output image because even if you said the white pixels were the colors offshore that you wanted to mask out, I don't know what you want the masking color to be (e.g. black or white), and if "only save the open ocean" means that you will crop something from the image. Recall images must remain rectangular.

[dpb]

Just wait a week; it'll all be underwater and the problem will be trivial... :)