An inexpensive solution is to get a few wooden pallets and set them out in the water. They may float for weeks before they sink, but you can eliminate them sinking by attaching empty plastic bottles to them.

I anchor them in place by using a cinder block and a tether. Make the tether long enough to withstand fluctuating water levels if you pond is subject to that.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."