I'd start with a low tech approach : may not be so easy , depending on surface area of the pond, tohugh. I'd try to spread newspaper, three or so pages thick, across the surface... lay it on lightlty and as soon as the water starts to soak in, remove the paper. Do it in sections, trying not to disturb the surface of the water too much as you go. If the oilyness is only a thin layer that should soak it up without releasing any nasties from the newsprint.
I've just had a new oven door delivered (glass outer exploded the other evening just as David, 'Dr Rock' was here for his supper before our SRGC Meeting!) - it's been packed with large quantities of crumpled unbleached paper... perfect for your task if you could get it.
