I'd put a mess of bentonite in the possibly get it into the cracks. Then I'd call the dozer guy and tell him you had a hole in the bottom of your pond and don't want to wait. I'm sure he understands that it may never hold water and that he is the guy that dug it.
Bentonite is OK but is iffy. I would cover that hole and everything close to it with a couple of feet of well packed clay.
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
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