especially  in fast water areas.  When the giant stoneflies hatch they crawl out of the water and hatch on the bank. They often accumulate in large numbers in the streamside vegetation at the edge of the water.  Here they are actively crawling and mating much of the day.  This activity will land many in the water where they will float for awhile before they get back to the bank.  Trout know this and often station up right on the waters edge to intercept them. An angler who fishes his fly up under the trees and along the edge of grassy areas will often be rewarded. A high floating fly like the Improved Sofa Pillow is often best for this kind of fishing.