A few years ago I had someone with a longarm trackhoe dig part of one of my ponds. I had him take the mud and dump it in a field above the pond and fill in some holes and the guy later showed me pictures where he went to a housing development in the winter with the pond drained and used his trackloader to dig the pond out. I would recommend you look for someone with a trackhoe since it can reach out a good bit and dig further out.