A couple of thoughts from a non expert in this area.

First, shoreline vegetation "generally' has deep enough roots to survive.

Second. In the pictures, it does appear that the leak is at the area where your "blocks" sit on the actual dam. If that is true, I don't think you would lose any more water than where you are now. And, at this time of year, you're probably not get rained out during the repair.

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