Studies by CWU professors are currently being conducted on the Yakima Rivers stonefly populations.  This study, which has been under development for several years now, documents the life cycle and history of several varieties of aquatic stoneflies that reside in the Yakima system during various times of the year.
When we think of stoneflies, we assume that they are a constant food source to the fish throughout the entire year much like mayflies and caddisflies.  This belief has been proven untrue by biologist at the university.  It has been determined that the stonefly species of the Yakima River, use the ground water that feeds the river to travel back and forth from the main stem to the plateau of the Kittitas Valley. 

Yakima Stonefly Species

 1. Skwala Stone
 2. Salmon Fly
 3. Golden Stone
 4. Yellow Sallie
 5. Short-wing Stone
Several ground water wells have been established several miles off the main stem of the Yakima and are monitored throughout the year by biologists.  What they find is amazing.  During specific times of the year, these monitoring wells are full of stonefly nymphs.   When the out migration to the main stem of the Yakima begins, the wells become stagnate of these aquatic life forms.
What triggers the out-migration?  This is the biggest and most fascinating question on the minds of the CWU professors.  Stay tuned for more details.
So we now can see why stoneflies at certain times of the year are an essential part of the Yakima River rainbows dietary consumption.  It is at this times of the migration from plateau to the main stem that is most important to the fly fishermen.