Blue Winged Olive

Baetidae

These prolific Mayflies can be seen on the Yakima all seasons of the year.  Blue Winged Olive is a generic name for mayflies from the Baetidae family and includes muliple genera and species.  The best hatches occur in March and April and again in October and November, ranging in size from #24 to #16.  A smaller emergence occurs during the summer months in sizes 22 and 20.  BWOs nymphs are swimmers and live in a variety of moving waters, but prefer slow to moderate runs and riffles. 

Western March Brown

Rhithrogena morrisoni

Rhithrogena nymphs are clingers found in moderate to fast flowing runs and riffles.  Emergence generally begins in late March and continues through early May.  These are large Mayflies which can produce some of the Yakima's  best dry fly fishing for large fish.     

Pale Morning Dun

Ephemerella inermis, Ephemerella infrequens

PMD activity begins in May and continues through July.  Infrequens emerges first, followed by and overlapping inermis.  This can be an important early summer hatch, but varies from year to year.  PMD nymphs are classified as crawlers and inhabit slow to medium sections of the river.