Thanks y'all.
I anticipated the comments and I have no intention to do anything but leave this Mommy fish and her nest alone. Still, I was hoping for ideas on how to discourage future fish from building nests in this particular area.
There are these things called Lakemats (
https://www.lakemat.com/lakemat-pro/) that are designed to prevent weed growth. While weed growth isn't our problem, I'm sure they'd prevent fish from building nests in our little swim area. I would set one or two in place in early spring. But, they're costly and I have no idea regarding durability. Maybe a simple tarp weighed down by two-bys would do the trick.
Ironically, I myself encouraged the fish nesting. When we bought, this 'swim area' was just a bunch of six inch or so rocks. Not a comfortable place to walk or congregate at all. That first two summers, I removed all of those rocks by hand which left the current pebbly bottom that the fish like.
I suppose we'll continue as we have for the last seven years and just hope for the best. I may even install an underwater sign with arrows pointing left and right advising that our neighbors have more hospitable nest building sites.