Not an expert either...but I would think the muck would be better left alone (if you cannot get it out) rather than loosing depth by trying to bury it. Not to mention the difficulty in burying it... 2 cents and hardly worth that.

My other thoughts...

I'm having some difficulty imagining how you would successfully get a layer of clay over even 1 foot of muck especially if it is still water logged. You would have to mix in alot of dry earth to even be able to walk across it let alone drive a piece of equipment over it and then you could scoop it out.

Can you cut a road on the grade to use to move the far end dirt, or a shelf along one side below water level? If so, you could leave the remaining water and muck. Maybe it's not ideal to leave some muck behind, but the muck that's already been removed would be a great improvemennt. Let's face it, there are alot of ponds out there that are loaded with muck and are still a desirable asset. Leaving some muck behind would be a shame, but it's not terrible...it would be at the very bottom which would not contribute too much to FA, if any, you dont have to have the extera depth..just saying.

Can you pump the water out so that it dries some and at least create a path through it to get to the dam cut? Maybe back-hoe a trench through the dam cut to drain the rest of it.

Just some thoughts that you might be able to spring off of.

Fish on!,
Noel