Is it possible to cut down some trees to facilitate some wind hitting the pond, and maybe some sunlight hitting it in the winter?

It sounds like you might have electricity at the pond?

Perhaps some type of horizontal water mover like Dwight uses could help?

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."