“Before I speak, I have something important to say” — Groucho Marx
Generic hatch charts suggest Green Drakes, small and large in size, start to hatch moderately when a stream tempetature reaches 52-54F (11-12C). The sweet spot is noted to be 54-58F (12-15C) for the most prolific hatches. Yet, there is one stream I fish where I see Drakes at 46F (8C). That’s several degrees cooler. I’ve noticed the key to the hatch on this specific flow is direct sunlight flooding the river bed/bottom. Once solar exposure happens it seems the nymphs are “ready to go”; ready to emerge. And it is not because the water temperature increased significantly in sunlight. On a sunny day I have seen it climb only 3 degrees by late afternoon.
So hatches can be river specific. This particular hatch appears synchronized to the valley’s lighting conditions once water temperatures pass 45F (around 8C). Once light floods the river I start looking for drifting Drakes and hopefully a response from the trout. Cloudy cooler days are never as good. Late afternoon mountain shadows seem to squelch the hatch. The trigger appears to be sunlight.
Speaking of hatches…there have been few dry fly opportunities this summer in my region, at least on the dozen or so rivers that I have visited. Bug life has been on the decline for years and this year it seems to have dropped off a cliff; it has “tanked” on most rivers…even on the generally reliable local tailwaters. Hopefully it will improve somewhat before the end of the season. If you are a visiting angler and want to be successful, you’ll have to be versatile in your angling methods.
trout on dries 
Hi Bob,
I remember reading somewhere about how excessive daytime heat can cause insects to sometimes hatch more at night. If there’s been a heat wave, maybe this is part of the reason for seeing fewer hatches during the day? Nice cutties in your pics. Have you been fishing in BC? – Vic
Vic: I’ve read that too and experienced it during the “dog days of summer” ; however, water temps have been good/cool for this time of year on tailwaters and in mountains. Lower oldman is just now starting to experience pmds …hatch may have been suppressed by higher flows than usual thru July.
Yes, been on Fording and just started fishing some other creeks in BC as it has taken time for them to become wadeable…too fast. They are still fast. One was pummelled by the deluge we had several weeks ago…pools filled, altered…trees down. However, still catching some nice cuts…also fished Elk…it was challenging on foot as healthy flow. Caught bigger fish elsewhere.
Hope all is well. Thanks for info, fishing advice re: heat wave and evening, night hatches.
bob
Just returned from fishing your area, both in BC (Elk tributaries) and AB (several rivers in mountains, foothills and prairie). Insect activity – aquatic and terrestrial – seemed way down but this is my highly unscientific observation based on my notes and photos from prior years (limited sample size). Always looked forward to the Western Green Drake hatch in BC. There were enough to get the cutts looking up, but prior years it created a frenzy. Most likely because I had over-prepared with plenty of fresh WGD patterns! One prairie river was entirely devoid of young grasshoppers, though I didn’t expect to fish hoppers. Even the ever-reliable foam parachute ant didn’t draw much attention.
Consensus among folks that I spoke to was that the AB side got scoured from the floods. Seems that stoneflies came through it ok.
But….I can’t wait to get back!
Greg: I think your assessment of insect situation and feedback you reveived from others is accurate. I’ve seen very few fish rising this summer esp in Alberta. On one tailwater, lower Oldman, just recently the pmds are happening. Water was too high before. It is still somewhat high for august and dirty looking. Some fish up…just last week or so….but still not great, so far.
So a tough season…not the best. Hopefully you made some good connections and when you return in future there are more insects emerging and targets. I live here and have struggled to find dry fly activity. Sounds like you covered a lot of diverse water (types)…got to do that when things are tough.
Thanks for taking the time to report…enjoy the upcoming Autumn and angling back east.
bob