Originally Posted by Fishingadventure
Clean ( Dredge ) and Clay liner . Myself, totally with JLudwig . irregular shape and island makes liner very difficult . Hopefully with 19% Clay soil you can sheeps foot the bottom after removing grunge . Resulting in a very slow absorption rate . Get all stones, all roots , all sand veins, gravel veins removed or dug out and packed with clay to seal . All "natural springs are also natural drains during dry weather " . 1" per day without a good liner ? You may get it down to 1-2" per week with good Sheepsfoot. The Well for this size may be reasonable supplement. Save up the cash if necessary. God Bless You and Yours.

I was watching some videos from Natural Waterscapes, and I thought they said ideally clay content should be above 30%. The water level was about 12" higher than it is now (in the photos) to where I filled it to test the rate of water loss. I can only assume it is worse if the pond were to be filled completely.