I've heard of a company that uses large filter bags and a pump to suck the muck out of ponds, but I don't know what it'd cost. I think it was on "Dirty Jobs" for one episode.

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).