How large is the pond?

How moist was the soil when it was built? Did it have enough moisture to pack well?

You may not have enough clay to adequately cover the sand but I doubt that. It's possible that you missed a spot or a spot didn't get adequately packed.

But, if it stops dropping at the spot of the hole, I would ASSume that is the problem. I would certainly start there and pack it.

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