the round planter in the back yard was what I suspected, it's going to house our turtles and goldfish when back up and running. concrete is in great shape, unfortunetly I suspect it cracked after it was backfilled and allowed to freeze
I live in indiana, so the pond will be drained for the winter.
the little round spot on the bottom left of the pond is a drain to the storm sewer so draining and cleaning will be easy.that's how I got it so clean for the pic, the drain takes more flow than my hose could put out for several minutes. It looks like it used to have a pipe threaded in that was cut flush with the bottom, which I suspect was up to the water level.
I'm not sure what the center pipe is as there is no intake for a fountain, but when I tried to clean it out, I found I could push water into it for a few seconds until it backed up, then water would run back up and out for a few minutes, maybe a gallon plus of water input and return which is puzzling. I'm going to dig around the perimeter and see if I can find some plumbing. maybe it had some sort of well or cistern feed into the pond and drain into the storm sewer.