Riffle, run, pool.
Although that is an accurate overview of holding water for trout, it is very general. That basic illustration is akin to saying that America is a beach, then some mountains, plains, little mountains, and then another beach. It is true, but there is much more nuance involved.
This matters because holding water describes the places that usually hold trout. They are the spots that you want to focus on when fishing, because they have the highest likelihood of yielding a strike. In almost every river, finding them requires a nuanced approached.
Even the smallest mountain creeks have a very diverse range of holding water. What this can mean for the angler is: trout can be caught anywhere. Depending on the season, fish will be found across the width of the creek and in every depth of water. Fish will be at the bottom of pools and fish will be in skinny water right off the bank. While there are some rules of thumb that can be observed, catching that one outlier of a trout makes hitting all the spots worthwhile.
The trout that live in smaller rivers have to be opportunistic. Particularly in the high gradient streams, a fish only has so many options. Predation, water conditions, and the presence of other trout dictate where any individual fish will move outside of the “most likely” zones. Brookies, rainbows, cutts, and browns all respond in this manner.
There are also totally normal environmental reasons for fish to settle down in spots that look less exciting. If a little run off to the side from the main current provides adequate food and shelter, that is enough for a trout. Perhaps the current is gentler, and their calorie expenditure versus intake ratio is ideal. They aren’t looking to conform to our expectations – they are looking to survive as efficiently as they can.
Consequently, the fly fisher who is observant of the details will be rewarded. This way of angling doesn’t mean casting your fly to every square inch of the creek. It entails reading the water at a level that goes beyond riffle, run, pool. Noticing small seams and undercut banks is vital. Overhanging cover and gravelly side channels aren’t as enticing as the plunge pools, but they offer everything and more that those normal spots do.
It might mean noticing where the depth increases against a bank in a riffle. Or, a small diversion next to a big waterfall creates another plunge and some slack water away from the main channel. Sometimes, it is an unassuming outlet from a major pool that funnels enough insects to feed a healthy trout.
Most of all, it means slowing down. It means thinking and assessing. It means not just fishing the holding water that usually has a trout or two.
This approach, the “fish every spot” technique, is really suited for water that you can spend a lot of time on. Whether it be that the creek is just down the road, or you have a few days to really explore, you can absolutely employ this when you have the luxury of time. If you only have a few hours, or you are on legitimate excursion, you have to make some choices. The deep pools might be your only areas of emphasis. That is, after all, a high-percentage game.
If you do have the time and diligence, you will experience the benefits of looking to the secondary or tertiary holding water. Trout only adhere to the conventions of food and safety. Those will trump a picturesque, deep hole beneath a waterfall any day.