Thanks for the idea. My husband did try to make what I called a "redneck" heating system by pumping water out through some hoses that were on panels for an attempt to provide solar heat. Our pond is 30,000 gallons, so I don't really believe it ever had any impact, but he swears it did. I really just want to warm the temp 5 degrees. Part of the problem is that the pond doesn't get in full sun until after noon and then looses sun around 5 pm- so if we just cut down the beautiful 100+ year old maple that shades it in the morning it would probably solve the problem. :) Which we are not going to do of course.

What about if you already have a pond, with springs, and wildlife (about 3/4 acre in size) and you want to make part of it into a natural swimming pool. Can that be done?

You may be able to isolate part of it with a stone wall or sandbag wall, to keep ir cleaner, but it would be tough to keep it as clean as a closed system.

Why is that?

To isolate it and keep it cleaner. You still habe the challenge of keeping up with wster quality of the whole body of water.

If you could wall off a third of it, would that work?