On Friday I guided Mark on a Farmy-Hous doubleheader. While the air was sweltering, the Farmy was pleasantly cool — and the fishing downright cold. We were nymphing, and in two high-probability runs we could only manage to stick one fish. In fact, we shared the water with close to a dozen anglers at various times between 12:30 and 3:30, and we saw only one other fish caught. Hatch activity was slow to non-existent. Feh. Off to the Hous.
Which didn’t fish much better — at first — and was a totally disgusting sweat lodge into the bargain. First spot in the TMA: blank. Second spot: a few customers. Third spot: Really? Nothing? OK, nothing until 8:15, then the switch was thrown, but even then we weren’t exactly lighting it up. Nonetheless, a strong finish to a tough day, and Mark did a great job of working through it.
Yeah, man. That’s what we like to see. The Countermeasures pattern did its usual reliable work at dusk, particularly in frog water and along the edges. Before dark, we had our best action in the “hot” water: bubbling, gurgling oxygenated flows like this.
currentseams.com 
Had the same experience Friday and packed up my camping gear one day early and left after the marginal to non existent evening hatch which I waited around for and fished till dark.
Exception- in the blazing sun after lunch Friday in a flat run after the campground pool, I saw a pod of fish sipping something at the surface. Only able to stick one with a size18 Olive F fly.
BTW-Thursday evening before and during a light sulfur hatch used 3 wets and stuck a nice brown and something you do not teach 😦 What to do when two fish are on you line at the same time lol Never happened before for me.
Extreme heat will do that, even to a tailwater. Hooking multiple trout on the same leader is far more glamorous sounding than it is a matter of practical course.