A Natural Swimming Pool in GA red clay?

I have been wondering how to go about building a natural pond/swimming area. I have a place on the keyline of a slope that seems to have plenty of rainwater running to it. I would love to just dig a hole and have it fill up, but I doubt it is that simple. How do I seal it? I thought of using bentonite clay. I have also thought about trying to create gley(sp) an anaerobic layer of straw covered up with more clay.

There are a million questions that come to mind. I have dug a couple of small holes where we catch some runoff from a grey water system. These are not particularly pretty, but they do seem to hold water well, after they acquired an abundance of leaves on the bottom.

Okay, I have gone through a number of the other threads and it looks like I may have the wrong idea. It does not look like it is a good idea to catch runoff water, if I want a nice natural swimming pool.

Hi Jason,
Yes, runoff water is not good for Natural Swimming Pools because of the nutrients it brings in. The pool should be constructed to prevent this entering.
There is no reason why any lining technique shouldn't be applied to Natural Swimming Pools. Clay pools should be deeper to reduce the sediments kicked up by swimmers. A synthetic liner is easier to install and easier to clean if debris becomes an issue.

Yeah, I'm putting my two cents in a few months late..

My opinion is that using run off would not be a problem in a natural swimming pond, as long as you take care of the extra nutrients and silt.
Direct any run off water into a natural filter before it enters the pond. Gravel and sand filters are good for this.

One way to make a natural swimming pond is to divide the entire pond into a swimming area , and a "nature area". There would be a wall under water up to
just below the surface.
The "nature" area would contain plants to clean out the extra nutrients, the wall would prevent the plants from taking over the swimming side.