Unlike the spring blue-winged olive hatches across Alberta, fall olives almost always bring trout to the surface and the head hunting game is on. Fall hatches occur from mid August through early November across the province's streams. Nymphs of blue-winged olives inhabit gravel & rock - moderate flowing riffles are prime spots to expect a hatch each afternoon. Fall hatches can start any time after 1pm. If it's cloudy, cold, and wet, chances are great the hatch will be heavy and occur later in the afternoon so be patient. But also be prepared as drizzle or snow flurries are best. Emergers' wings take longer to dry due to the cool air and duns will drift longer on the water, allowing for methodical trout feeding. This works well with brown trout especially, as they tend to feed heaviest during times of low light. Rainbows often move to the edge of riffles to feed where their gentle sipping can be mistaken for smaller fish: don't be fooled!
On popular waters where trout have likely been caught several times each season, you may have to use flash, wire, beads, or other subtle changes in your nymph patterns to induce a trout to take.