This hatch of Mayflies begins sometime in later September or early October on the Yakima river. They are a flat headed Mayfly measuring between 5-20mm. The adults have two (2) tails while the nymphs will sometimes have three (3).
This species is important to the angler because it is fairly common and the dun and spinner concentrate their activity in a two-hour period in the evening. Both male and female spinners are available as food for trout as they mate just a few inches above the water.
Nymphs cling to rocks and are very poor swimmers.
Order Family Genus Species Body Color Wing Color Emergence
EPHEMEROPTERA Heptageniidae Cinyana Dimicki Pale Yellow Tan Barred Evening