Where do you live?

I think a garden might look odd, given the rest of your garden. I'd go with a small, weeping tree. Japanese maple? Weeping cherry? Pick one with a root system that can withstand what it's going to be planted in.

We filled our pond in with dirt to the level of the yard and planted grass in it. Took out the bushes that were around it and you would never know it was there.....such an improvement to look at a nice level lawn now. Could you build a deck or patio over your pond...looks like what you have means more work?