That looks like a job for an excavator!
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. 
