You can get electric sump style pumps at the tool rental at Home Depot. They have a fairly decent flow rate, but nothing close to a gas powered pump. It would take a couple weeks to drain a pond that size down 3 feet, but noone would know you were doing it. Maybe you could rent 3 or 4 of them, and run them all at the same time...

Just an idea.

But you cannot set these pumps in the mud you would have to suspend them somehow in the water column.