Here are some closer pictures of the soil in our pond nostr:nprofile1qqs8ja6sqsw3xe4gp4z7zvxgx8c9v26lwfnxv2c84nh4ph25r0az2dgpz9mhxue69uhkummnw3ezuamfdejj7qgcwaehxw309a3k2mrvv9ezumn0wd68ytnhd9hx2tcpzemhxue69uhkummnw3ex2mrfw3jhxtn0wfnj7ufszel. It is clay from the light part down. At least 5' I have dug so far. 
Discussion
I see some low-chroma grey colors on the ped faces, so it's holding water at least a few months of the year.
You've got clay. Just need some compaction to seal it up. If you have the equipment to do so, push some of the clay from the bottom up along the sides to form a clay berm. A sheepsfoot roller is best, but driving wheeled or even tracked equipment over it is better than nothing.
If you don't want to go the equipment route, pen some hogs or ducks in there for a few months.
