So we witnessed an odd phenomenon in our pond last spring and it was repeated to lesser degree this spring. I wish Rock Doc was still posting.
The pond behind our house (about 5 acres) is only about 2-3 feet deep with a very mucky bottom. If you fell in you might drown because you'd sink 3' in the mud and then another 3' of water will put it above most of our noses (maybe not bb's). The level has been down the past couple years due to drought and the drying up of what had been a consistent source of water flow into it.
Last spring as the ice started to melt, I could see sticks and mud being exposed. I was baffled because while it was low, it wasn't low enough to show bottom. Same thing has happened this spring. Last spring I finally figured it out. The ice had frozen all the way to the bottom - and INTO the bottom. When the ice on top started to melt, this muddy ice floated up, forming a big dirtcicle that floated on top. Just a lovely look to the pond in the spring. Fortunately it is already starting to melt and sink back to the bottom.