"Well, not much to go on but the builder says the pond is a "natural" pond and has been there for 20 years."

-The live trees that seem to be 'in' the pond don't seem to back that up, however, as F/Rod suggested, maybe it's at high pool due to rain.

"My agent said one thing that's done to control the size (outward expansion) of ponds is to burm around it. I kind of like that idea aesthetically as well as from the control of size. Is that good/bad?"

- A burm can keep water out too, and if the pond is filled by run-off, then the burm/berm would stop that from happening.

With the water that muddy, the only way to know the depth is to go out on the water and test depth with a rope/string and a weight.

You may be able to call up some historical satellite maps and see what the pond was like over the years. Might give you some peace of mind.

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."