I would stop at your counties NRCS office (part of the USDA) and see if they have a list of pond contractors. Call them to get estimates on cleaning it out. The pond maintenance companies might just want to sell you chemicals and bacteria, not do the actual muck removal.

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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).