well I went out on the pond the last couple days before the ice started to melt. I drilled probably 20 holes and measured depth of ice and depth of water. I also got a 4" diameter PVC pipe and stuck it down the hole. I would measure how deep it went until it hit bottom with no force. Then I would add force the pipe and push it down into the much as far as it could go. Measured that delta. I did this in several locations and depths and found that it was only going down around 4-5". I feel that, that is a good representation of muck depth.