VICTIM WAS TRAMMING AN EXCAVATOR THRU A WET AREA TO GAIN ACCESS TO A ROAD CULVERT THAT HE INTENDED TO CLEAN OUT WITH THE MACHINE. THE LEFT TRACK OF THE MACHINE SLID OVER INTO A MIXTURE OF WATE R AND FINE MATERIAL MUD AND THE MACHINE TIPPED OVER ON ITS LEFT SIDE, CAUSING THE CAB TO GO UNDER THE WATER AND MUD. THE OPERATOR WAS TRAPPED IN THE MACHINE UNDER THE WATER AND MUD FOR APPROX