There's no absolute answer on this without draining and eyeballing. However, I'm concerned about digging a core down to rock and "dumping" dirt on top of it. Sticking the tractor downstream from the dam might be a good indicator of water running under the dam and on top of or through that rock.

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