EE OPERATING A MUD CAT DREDGE. CLEANING OUT SILT BASIN BELOW THE COAL YARD. EE THOUGHT THE HEAD WAS TRYING TO STOP UP, GOT OUT OF CAB TO TAKE A LOOK. PUT THE AUGER IN NEUTRAL AND LEFT THE ENGINE IDLEING. WALKED TOWARDS THE HEAD TO GET A CLOSER VIEW, AND CLIMBED OVER OIL THROUGH HANDRAILS, SLIPPED AND WENT INTO AUGER. LEG HAD TO BE REMOVED BELOW KNEE.