First, the character of the river and therefore, the feeding of the trout (the big ones) is affected by higher temperature and lower levels (current and velocity) of water, and by lower levels of oxygen. That is the primary factor in fishability of a venue – not the presence of other people, or even the presence of gleeful inner tubers. Our trout have their lairs established within the limited run of the canyon and the Dream Stream. They are not going anywhere. IF anything, they simply sink down and stop feeding for a moment when people float over them or a hard cast hits the water and a line combs their forehead. They don’t leave. They just hunker down for a moment. That is another story – the character of our high summer rivers.
Secondly, the character of a BIG trout in our summer river system, is one of hunkering down in a deep, cool, dark pool and sipping on larva and pupa… AND one significant other food: engulfed adult flies and terrestrials. The larger trout seek the deeper water to avoid the warmer currents. They have a limited amount of energy to spend on acquiring nourishment. The larva are actively scurrying around in the silt and moving from rock to rock seeking their own food – microscopic organisms and pieces of organic debris. The pupa of many many species are in a pre-emergent stage of absorbing oxygen directly form the water and retaining the oxygen in their wing sack, which will enhance their buoyancy when they age into the emergent stage. At this pre-emergent stage, their wings are beginning to bug out from the wing sack. So, the “nymphing pattern: to use is anything with a shiny, iridescent wing sack (bubble back emerger, flash-back emerger, etc.) with little sprouting wings. A perfect example of this stage (get ready – look in your fly box because everyone has these) – a bead-head pheasant tail pattern. Buy some flashback patterns, examine your flies to see if they are iridescent and have some sprouting wings.
OK – here is the big trick: In the height of summer warm temperatures and low oxygenation of the river, you need to present an engulfed adult fly or terrestrial to the big trout who is lurking and feeding their hole. Not a streamer – this fish does not want to invest its energy in chasing a crippled fry; this big trout cannot commence battle or compete with other trout during this critical stage. The most a big trout is willing to do is hangout and sip on tumbling emergers and pre-emergent pupa. That said, the large trout knows that it can get a huge nourishment bite (Pokemon Go comes to my mind) when an adult fly like a caddis or a terrestrial like an ant, hopper, or beetle comes slowly tumbling along in the current near to its lair. A large trout won’t come to the surface to take a big fly (too much energy spent) but it will venture out of its lair to snag an engulfed larger pattern and then slip back into its dark lair.
What does this mean to the angler?
It means, get a large, chubby or rubber-legged pattern or hopper down in the current that feeds off of a cobble riffle and pours into a bend with a long, deep, run – a bend with a large undercut. Put the submerged fly in line underwater with the hunkered down bug trout. Fish the hopper or chubbie below a heavy split-shot weight and high-stick it through the deep holes.
The submerged large fly is more attractive to a big trout than the tiny larva and emergers in the current. A large trout will leave its lair to snag a big fly as long as they don’t have to come up to the surface or battle the current.
That said, I hope I have emphasized that these large trout are in a conservation mode of survival. The warm, elevated water temperature and lower oxygen levels has the trout in a state of stress. When you catch one and drag it out of its lair, the level of stress verges on critical. I would urge you to walk the trout down to softer water and release it with a hemostat underwater without touching it – no net. Just walk it down to where the water is ebbing out against a shallow shore, lift the trout head out of the water and slide the hemostat down the line until you can grab the shaft of the hook and with a quick twist pop the fly out of its mouth. A trout under this situation likely does not need to be resuscitated by hand – just let it drift on its own accord back into the current. Avoid touching it at all.