What about doing thin lines, like the raked lines in a sand garden? Or bamboo bordering, with thin green leaves? Perhaps even a koi or two swimming below some floating lotus blossoms, similar to the drawing below:
On a side note, there is an incredible Japanese garden and gallery near my house that I went to this weekend with my girlfriend. If you're still working on this mod, I could go shoot some reference photos for you, there are some great scenes there to shoot. Great flat stones creating a walkway across the pond leading to an island with a wooden bridge and a huge artificial waterfall. Very neat place.