This pattern is tied on a size 14 hook and is a general upwing dun imitation.  The deer hair body, heavily hackled abdomen and yellow tail make this fly ideal when fished in rough water either in a lake or on the river. The yellow tail, as the name suggests, can make this fly irresistible to those difficult to raise lake trout during a hatch of upwinged flies. If used on a lake the track of the rising fish should be noted and the fly-cast 6-ft in front of the last rise. If used on a river it should be presented drag free to rising fish. Early morning or late evening is the best times for use, during the warmer months of the year.