I would have never thought about #3. I did that when I
cleaned out my sons pond and never thought anything about it.
I can sure see where #4 could be a problem, especially in areas where the topsoil is deep. We have such shallow topsoil here that usually the water hardly makes it up to the topsoil level in lots of ponds. That would be a good situation to push some clay up from the bottom of the pond and cover the topsoil area around the top as the pond is being built and compacted.
