Over time, ponds fill up with sediment (silt and muck) and most of the time vegetation starts growing within this sediment.  Dredging is a method to clean out a pond by removing the sediment.  It can be done by digging it out with an excavator or pumping it out with a dredge.  The sediment is usually completely wet and takes time to dispose of it.  It can be placed either nearby or hauled away to get rid of it permanently.  Dredging with excavators usually requires skilled operators to stay on a surface where they do not sink in the mud.  It is not typically performed with a bulldozer pushing mud out of the pond like traditional dirt work.