Stardock is working on a new Aquarium Desktop but we need a bunch of high quality aquarium backgrounds to include. We've looked around and have not had any success finding any (we need backgrounds that don't have any fish in them already for one thing).
So we're looking to the community to see what can be produced. If you'd like to take a crack at making good wallpapers that have an aquarium (or even underwater) background that you think would fit this project, let me know and send them. If we use them, we'll give you credit in the docs, a free copy of the program, along with a free copy of Object Desktop (or an extension to it).
My email address is bwardell@stardock.com.