I don't understand your area and know absolutely nothing about a pond being fed from below. Maybe the shale and/or rock strata are below some kind of groundwater that is being prevented from moving by the heavy duty clay. Does the neighbor say that the pond will go to full pool from the bottom? That sounds artesian.

I don't know the answers. I'm not sure I have ever heard of that type of pond environment.

Anybody??

It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.

Without a sense of urgency, Nothing ever gets done.

Boy, if I say "sic em", you'd better look for something to bite. Sam Shelley Rancher and Farmer Muleshoe Texas 1892-1985 RIP Grandpa