Draining the pond is pretty easy. Was the bottom/sides of the pond compacted when they finished digging? If not, then if it was mine, I'd drain it, compact it, and then refill.

I haven't seen (or heard) of any leaking ponds being fixed permanently by sprinkling bentonite on the water.

You can rent a gasoline powered semi-trash pump that can move a LOT of water per hour. I've drained dug ponds of 1 ac in size with a 16,000 gph semi-trash pump. Let it run for a couple of days and the water was gone. If the pond is leaking, then the water will go down even quicker.

www.hoosierpondpros.com

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).