I think you'll most likely have to re-core the dam, which would mean draining most if not all of the pond to minimize the chance of having a blow-out when the core is dug in the dam.

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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).