My pond tapers to a point in a place where there was an old earthen spillway, and I want to fill that part in to round it off. There's about 3-6 inches of muck over hard ground underwater.

I'll be piling about 1.5 feet of dirt to bring up to grade. It seems best to scrape the muck before filling. BUT that'll be a huge pita. I'm sure I'll get the tractor stuck no matter how careful I am. This area won't be used for driving. Can I just pile my fill on top of the muck? What if I run into deeper muck? Are there any other considerations other than having relatively solid ground for my tractor?