Just a thought....
Before you rent the trash pump, buy enough pipe/hose to re-route the water that is coming into the pond to go around the pond. Then all you'd have to deal with is what seeps into the pond from underground.
To measure the muck, take a 5 gallon bucket lid. Attach it to a pole (rigid electric conduit works) and push it into the pond bottom. Mark where it stops. Remove the bucket lid, or use another piece of conduit and shove that into the pond bottom. Mark where it stops. The difference between the 2 marks is the depth of the muck.
If you get the trash pump, you could make a venturi suction system like
this Muck is relatively light and could possibly be sucked out of the pond.
But, have a plan in place where to put the muck that you remove. I think a pump and excavator would be the quickest route, although probably not the cheapest. Careful with the tractor, they get stuck easier than they get unstuck.....
