Pic 1: the "green spot" is the area where I think the pond could be build: the water does not drain and stays on the surface and the grass remains green even in the winter:

Pic 2: Close-up of the green wet spot:

Pic 3: Marshy area in the woods behind the "green spot" where the excess water from the pond could be redirected:

Check with local federal government, may Ag Dept. They may have some info for your area, may send someone for free to test soil conditions, maybe even kick in some grant money if you keep the pond as a benefit to everyone, like a wetland.

You couldn't really keep a clay pond filled from a hose. Unless you're talking 24/7 full on. If you had access to a large water supply and big pump than sure.

How deep you want to go really drives the design. If you scrap the topsoil off for a shallow deal it won't look good for at least a few years. Takes awhile for plants to grow in clay. I had a couple of other scraps and all acted differently even though they were just a couple hundred yards apart. One always had muddy, milky, water from the clay. One never did anything too interesting. The biggest was a real pond.

Since you don't want fish you can scrap off the topsoil, then scrap out some clay, maybe 12", so now you're down 18, 24 or whatever inches. Push the topsoil back over the entire deal. Then plant marginals around and inside. Search for "vernal pools" to see how these things work.

Many pond plants, called marginals, will say something like , depth 6". But generally this is the maximum depth. Almost all marginals do better above the water line but in wet soil.

Based on my experience I wouldn't go in between. I'd either go with a real year round pond or a vernal pool.

If the source of the water is rainwater runoff, and it is being held by the clay layer, you would expect far more variation in water level. Also, if the layer below the good clay (the lighter colored clay) is more permeable, then digging through that top layer could reduce or eliminate the water holding capacity of the pond.

What if you started by just digging a fairly small hole out with a shovel, through the top layer of clay, and see if it fills with water? Better yet, two holes - one that stops short of going into the lower layer and one that goes through to it.

Search for Dewponds, Million ponds, Sodium Bentonite, puddling, clay lined ponds and clay lined canals as a start, Vernal ponds, too, of course(I forgot about that one). The clarity of the water will depend on how well the clay is compressed and the turbidity of the water. You might want to check out bog filtration, too since you want to utilize runoff.

You need to have a thick layer of clay that is free of intrusions such as roots, rocks and strata of other soil types. To retain water for a good length of time the clay needs to be compressed or puddled. The success of a clay lined pond depends on the proper material and puddling for the most part so you need to do a peculation or perc test to start so you know what is needed.

The DNR, in some areas may be able to give you some info. English Dewponds go back centuries and the British have been encouraging a resurgence for some time so their info is very good.

Sodium Bentonite is the clay commonly used to line most farm ponds and runoff retention ponds.

The success of a clay lined pond depends on the proper material and puddling for the most part.

To avoid mosquitoes you could check out solar fountains although they are not very efficient.

I would guess it's pretty rare to have a better draining layer beneath a clay layer. Otherwise I'd assume the fine clay would have washed into the pores below. In my limited experience clay was just above bed rock but could be very deep.

This thread reminded me of my old ponds, 40 years ago. So I went onto Google Earth to see if they were still there and they are. But now with big trees around them. One of scraped pond was to keep a spot from flooding and nature took it back to the way it was originally. It would be cool to go back there someday.

Changes of the ground can take centuries to happen naturally or it can happen very quickly as in a flood. Sometimes it doesn't happen at all or takes a millennium. Some strata can be very thin or oddly shaped or very thick. The ground is a history of the land.

To 12amilou - to clear up muddy water, if you're not willing to line your pond to prevent mud from leaching into the water, you'd have to install some sort of circulating (pumping) and filtering system. If you're looking for a summer swimming hole with clear water, that may be your only hope. But once sunlight penetrates clear water in the warm spring months, algae will be able to grow, which is why swimming pools use chlorine. Also, if you have leaves falling into it, that's going to create gunk that will need to be removed somehow if you want nice clear water. Or just swim in muddy water. Lots of people do it.