This pond can be fixed it is just a matter of how much money you are willing to spend to fix it. I would start of with bentonite around the area you said you found the leak after the pond has been emptied. Then just see how that goes. If there is no change then you have some decisions to make.
Look into how much money it will cost for a liner and how much it cost to haul in clay, spread the clay and compact the clay.
Also are there alternate sites on your land that do have a steady supply of water you could tap or dam up. Might be cheaper to simply start over somewhere else.
