They have guys that pump concrete. It probably won't be cheap to pump the pipe full of hydraulic cement, but it'll be cheaper than fixing the pipe or repairing the dam. I'd look into a concrete pump.

To inspect the pipe, plumbers have cameras on a long snake to inspect sewers.

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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).