Bright River, Big Bugs: Mecca Flat, Deschutes River Professional Review and Guide
"Swarms of enormous salmonflies hatch on the Deschutes River in June, filling the air and the water in an impressive spectacle of newly emergent life. Park at Mecca Flat and walk downriver along the trail. Carefully check the brush and trees along the banks for salmonflies that may be clinging to them. Especially watch tree branches that hang over the water.
At this time of year, the river’s trout population moves in close to the banks to feast on insects that fall into the water. If you hear and see splashes in these areas, it is almost certainly trout eating salmonflies. You will also see the insects flying along the riverbanks and over the water (they are slow, weak fliers), and if you are lucky, perhaps you may even see some emerging from their nymph shell. Salmonflies do not bite or sting, and they are easily picked up for a closer look."