I recently read that someone (esshup?) had a suggestion for measuring your muck depth.

They said to take a piece of larger diameter PVC pipe (2"?) and probe for the lake bottom. Mark the pipe. Then plunge the pipe as far into the bottom as possible and make another mark.

I believe the theory was that you should be able to work the pipe all of the way through the muck and the pipe only stops when you hit firm substrate (which was the original bottom of the pond).

[I was thinking of drilling a hole through both sides of the pipe (at the top) and inserting a 1' piece of rebar to make a good handle for driving and subsequently pulling the pipe.]