Question: I’ve seen these big fish at the bottom of the deepest pools, they’re refusing everything I throw, and I’m determined to catch one. What do I need to do?
Answer: It’s alright to leave them alone.
Fish are cold-blooded; they can’t regulate their own body temperature, they have to seek out environmental conditions which are best for their survival. Most fish species don’t grow throughout the entire summer. They have a range of temperatures which optimize growth. Above that, they’re eating just to stay alive- taking in enough energy to maintain homeostasis.
Those big fish in a deep pool are down there because it’s the coolest, most thermally stable, most groundwater-fed portion of the flow. They’re not eating because they’re not expending a lot of energy in still water- they don’t need to, they don’t want to, and dragging a streamer across their nose to elicit a territorial response isn’t doing them any good. Feeding them a zero-calorie Zebra Midge and then having them expend valuable energy on the fight, the photo, and the release isn’t doing them any good. To crib a line from John Gierach: sometimes, they need the sanctuary of deep water.
We talk a lot about values like C&R, barbless hooks, and leaving fish on redds alone. If a fish spawns in October but dies in June from a combination of high water temperatures and angling pressure, we’re undermining our own cause. Think about it. Pay attention to the temperature. Go on an overcast day. Make it a half-day morning trip, a night trip when temps have cooled off, switch to bass or carp or gar that can stand higher water temperatures. But know what you’re doing, and the effect it has on the fisheries you value.