Lake olive duns are found on most ponds, lakes and reservoirs but really large hatches are mainy seen on clean, natural lakes.  There are a number of different species but all the duns are very similar.  They tend to be dull browns and olives, which means the generic patterns are suitable for most waters.

 

On damp or humid days it can take a long time for the duns to leave the water's surface.  This can cause a feeding frenzy in the trout and it pays to watch for localised hatches in these conditions.  There are two distinct hatch periods in the year.  One in May/June and another in September/October.  Recent warm years have seen these two periods move to earlier and later in the year.

 

Smaller is better with these flies.  If you are not having any luck, and there appears to be a hatch on, a smaller pattern can often change a fisherman's fortunes.