I can not imagine the amount of work it would take to de-muck even a 1/2 acre pond with a pump. My 60 year old 1/4 acre pond was silted in such that the water was only 2 foot deep (originally 10'). The amount of muck that came out of it was massive, hard to explain...likely 400,000 gallons of muck...that's about 2000 cubic yards...that's over 150 common dump truck loads. And, with a pump setup, you would be sucking alot of water out with it (you could mostly drain your pond of water in the process and not have any water to fluidize the remaining muck). This would make the management of the muck very difficult unless you had a flowing stream to inject it into (I bet that's illegal anyways). Not to mention that most rental pumps are trash centrifugal pumps and sucking up rocks and such is going to destroy it over the course of de-mucking a small pond.
My pond had the dam broken in May (IIRC) by using a mini-ex, the break was dug deeper a few months later, and then a track loader was used to remove the muck and rebuild the dam in October...by the next may/june, the pond had filled back up and all was good. I think I had $4500 in the work (this included dressing the dam a yseveral months later to smooth it out to be seeded).
It's hard to think about draining a pond, but I believe it to be the most cost effective way to revive it.
