I'm no expert, but I do not think it will work well or be easy to push dirt over top of existing pond muck. Depending on how deep the muck is, the pond will have to sit for quite a while before being able to solidify enough to support an excavator or dozer. My pond had 2' of muck before hitting clay and it sat 3 months in summer heat before the muck layer was hard enough to be worked and even then, it was still very difficult to work in. I think your better off just removing the muck if you can. I put muck in two large mounds (one at each end of the pond) and later spread it around in a nearby field.. makes good fertilizer.