Im not sure about your area but from what I understand they have all but quit using ponds for geothermal systems here in MO.
Something about the soil hold and transfers temp a lot better then water does in the hottest of summer times and also holds tems better in the winter time.
I dont know all the ins and outs or the pros and cons, although I used to dig in quite a few services from the edge of ponds to new houses back in the day to not having or knowing anybody that has done it in a long time.

Have, however, dug in quite a few ground loops in recent yrs.

Directional boring in the loops is a pretty big thing around here recently, they can run huge loops out underneath woods or just about any surface you can imagine, without disturbing any surface vegetation.
Again, I know very little about the whole subject but my point is, do your research, dont take my uneducated word for it.
I always thought a pond water loop system should be a great idea.

All the really good ideas I've ever had came to me while I was milking a cow.