First the area where there is lots of clay.... how long has it been since you got lots of rain, I'm wondering if this area actually is part OF the pond and fills w water during times of heavy rains? The area may not hold water well (it drains out slowly aka a leaky pond) OR it may have just dried up some. The pole is probably there to tell you how deep the water is. I strongly suggest that you do one or more of these things.
1. Call the previous owner to ask your questions. If your realtor will not give you this info, you can talk to the neighbors or go to the county court house to find out who owned it last.
2. Talk to the neighbors who have lived there a long time. They can tell you how old the pond is, what happens when it floods, ect.
3. Call you local conservation dept for advice on what to do with it. They sometimes offer fish stocking days (you can purchase small fish to stock your pond, they usually have a few different kinds for a very reasonable price). Sometime they can do soil samples and tell you what you need to do to control algae growth, invasive plants, or how to fix a leaky pond. (Usually lining the pond with Bentonite, a type of clay.) ect.
4. Call someone in the area that works on wells and have them come out and show you the ins and outs of that if you can't locate a neighbor/previous owner to give you a crash course. You will probably have to pay a small fee for this. Sometimes on the equiptment you can find a name/contact of the previous company that worked on the well and that would be best. Some areas require reporting when a new well is put in, again call your conservation dept they would know who to contact for that. I think most places started recording most accurately in the 80's. You can find out who put the well there and maybe contact them if they are still around.
Also if you are unfamiliar w ponds and have kids,pets that are not used to ponds---They may appear to freeze over in the winter-but that layer is very thin DO NOT EVER walk out onto the pond-kids are very attracted to that-it is VERY DANGEROUS. Teach your kids to ID area snakes (aka water moccasins) And not to try touching snapping turtles which large ones can do serious damage if they bite you (lose a finger ect, I was shocked to see personally how powerful their jaws are
) Basically kids should not play unsupervised at ponds.
Next, remember that any pesticides, herbicides, ferilizers ect that you use, not just around the pond (obviously) but well away from the area, can wash down hill into the pond and throw things out of balance or kill fish/birds ect.