Please don't take my word for it!
Send a PM to Esshup, I think he has a groundwater pond and is an actual expert on the subject of ponds. Unlike me. I'm just an interested amateur.
Yep, got a groundwater pond. I don't know if I'm an expert, I defer that to Mike Otto, and other great dirt movers here on the forum. I just have a lot of experience with them.

My property has a high water table in the usual wet spring, water is 24" below soil surface, and it will stand over a foot deep in the woods. When we renovated the pond, it was sand to 11', then 1' of gravelly clay, then pea gravel for the next foot. Back to sand and finally hit blue clay at 22' depth. Not enough to line the pond, and a pond liner of that size was out of the budget. In some areas of this county, there is a 50' thick layer of sand before the clay.......
Do a search for "groundwater ponds" and you'll see some pictures.