In most rivers they use the skamania strain of summer run hatchery fish. These fish usually start entering the river systems in april-september and sometimes october depending on water conditions (drought). Once in the river they'll usually hang out in the upper reaches of the river where the water usually flows cooler during the summer and wait until nov-late january to spawn, then they head back downriver and back toward the ocean. At times people will mistake these downriver traveling summerruns as they will actually rechrome in the river system after spawing. A great way to identify these fish is by there snakelike appearance and they'll usually have lighter colored gills that have freshwater mites in their gills. A fresh steelhead whether it's winter or summer will have bright red gills and a full body as they haven't spawned yet.
Hope this helps.
Keith