Only a little concerned? Springs can be nightmares anywhere around a pond.

If the spring is truly behind the dam it might not be a problem but it is hard to tell. 1/4" drop isn't a big deal. The water is wicking back into dry soil.

Were there any wet spots when doing the core trench?

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