The brute was holding in a barely perceptible lie among the cobbles, finning occasionally for balance. While well camouflaged from above, he showed the unmistakable profile of a mature specimen: massive shoulders, enlarged jaw, deep crimson belly.
Holding my breath, I checked my backcast and threw at him from a crouch. He smashed the heavily dressed fly before I was even on top of my drift, and immediately tore off downstream with it, vaulting over two small waterfalls before I caught up and brought him to hand.
What sets this scenario apart from a typical storyline is that I was using a 2-weight rod, the water in question was flowing at about 9 cubic feet per second (cfs), and my trophy was a fantastically colored, 12-inch greenback cutthroat trout in Rocky Mountain National Park. To my mind, it doesn’t get any better than this. In my education as a fly fisher, I’ve come to realize that learning to fish very small streams effectively not only carries over to bigger water, but is also is a superb discipline unto itself. Structure and flow can be seen in miniature, stalking and presentation can be totally unforgiving, and food forms are not always obvious. The good news is that much of this resource goes ignored by the majority of fly anglers. Understanding the biological mechanics of tiny streams is a key to success, and there are three primary drivers: temperature, turbidity, and wind.
What is considered a “small trout stream” is somewhat a function of the region you live in, but in my neck of the woods, I’d say that anything in prime shape at under about 20 cfs qualifies. One of the crucial distinctions between this kind of water and your average tailwater trout resource is inherent. Small streams are, by definition, freestone biologies, largely comprising the headwaters and feeder creeks of major rivers. With little water volume or depth, they are subject to extreme temperature fluctuations, with daytime solar gain and nighttime cold having much more effect than with conditions on a typical reservoir outflow.
Periods of optimal feeding temperatures between 48 and 55 degrees are often short, three-hour midday segments at either end of the season. In hot weather, you might hit that temperature range by midmorning. Sunlight cresting a ridge upstream can raise the water temperature five degrees in the time it takes for you to rig up.
Because of this variability, trout can go from being entirely clammed up to voraciously opportunistic in a matter of minutes. Carrying a thermometer can take a lot of the guesswork out of gauging conditions, and provide time for other observation while waiting for your window of opportunity.
Turbidity (or, the degree of sediment in solution), is another factor to consider—and one that can sometimes work in your favor. While small streams can be subject to flashes of muddy spate conditions after localized rainfall, the opposite can be true as well. When larger rivers go off color, especially in spring, clear-flowing feeder creeks at lower elevations can offer trout their only respite from silty, heavy flows.
Even when it’s not raining, spring spawners such as rainbows and cutthroats can stack up in tiny creeks looking for clear water and a gravel bottom structure to dig their redds in. Spawning fish should be left alone, but after the spawn, these same fish often go on a feeding binge. If the food is consistent, sometimes these sexually mature fish will find a spot they like and decide to stay a few months.
Brown trout sometimes follow these spring spawners, feeding on the eggs of trout and suckers. After the spawn I target the same larger browns by throwing tiny unweighted streamers that imitate fry. A #14 Pine Squirrel Zonker pattern swept into a deep undercut in May can create an explosive result.
Smaller streams tend to cut through more localized geology than longer-running rivers, giving them specific pH factors and other distinctive qualities that can favor certain entomology. While reservoir outflows are typically excellent habitat for midges and annelids (worms) owing to a relationship with upstream stillwater siltation, a small headwater creek above that same impoundment can present a radically different environment, running down a clean granite ravine or flowing from a limestone cave. In these places, you might find excellent populations of clinger-type mayfly nymphs or free-swimming caddis larvae—both species that are generally intolerant of turbid water conditions and can live abundantly in the confines of a 10 cfs channel bottom.
Some small creeks are exceptionally rich in terms of total insect biomass. When this is the case, resident fish in the creek are usually fat and healthy. Downstream, fish in larger waters can smell the feed, and will move surprising distances to take advantage of it. Fishing in a small tributary of a larger river always holds surprises.
Because of the highly variable nature of small-stream freestone biology, the variety of insect types tends to be high in comparison to stable tailwater environments. Tailwaters generally produce huge amounts of just a few species, unsurprising given their steady temperature and turbidity conditions. This is the primary cause of the selective feeding tailwaters are famous for.
Freestone environments (especially small ones) are radically changeable, with many dozens of insect types staging for chances at conditions favorable to their specific adaptations. And while the insects in dam outflows are generally small in overall size—on the order of #18-#24—bugs in wild water tend toward the medium and large end of things, a happy circumstance that allows for presenting heavily dressed, high-floating dry flies in sometimes rough small-stream structure.
An exception to the rule here would be small streams that qualify as spring creeks. Flowing out of weaknesses in geology, spring creeks are notoriously rich in insects, the biologically natural equivalent of a tailwater below a dam. As the water coming out of the ground is the temperature of ambient earth (about 55 degrees) all year round, it provides stable conditions, at least in the short term, after its surface appearance. However, the total water mass of a spring creek under 20 cfs is still more subject to heating and cooling than a larger river, and conditions begin to mimic a freestone biology if the run is more than a mile or so.
Many river canyons have exposed water sources in the course of cutting their channels into aquifers, and these can attract fish even if they only flow for a few yards, where they then contribute to the larger river’s volume and temperature. During the hot drought summer of 2018, when water rights of upstream stakeholders took precedence, guides in the Rio Grande Gorge in New Mexico noted that various spring-fed creeks coming out of the walls of the gorge were making more of a contribution by percentage than in normal years, lowering water temperatures in the main river and causing fish to park downstream of the small confluences to enjoy the increased oxygen saturation that cooler water provides. Many famous trout fisheries in places like Montana, Patagonia, and New Zealand are actually spring creeks or have significant spring-fed contributions.
One afternoon in Rocky Mountain National Park, I was on a scouting mission to find new water, and stepped across a small creek that was more like a trickle. It was not more than 18 inches wide and running about 3 cfs under overhanging grasses. Just above my crossing point, I spotted a fin showing from under a bank in a corner pool the size of a turkey platter. After I managed to make a bow-and-arrow cast with a small hopper pattern, I was stunned to see a 14-inch Loch Leven brown whirl around and hammer the fly.
One hundred yards downstream, this tiny creek converged with a larger, oxbowed meadow stream that is generally silty by nature. On closer inspection, I found the clear, fresh water of the smaller rivulet was bursting with fat Ephemerella mayfly larvae under every rock. There’s only one reason a larger fish will tolerate the degree of danger tight, shallow quarters present, and that’s food.
While prioritizing the incentive of abundant food, trout in small streams are extremely attuned to how exposed they are to danger, and exquisitely sensitive to outside stimuli. Heavy footsteps on the bank—especially after a rain when the ground is saturated and carries sound—send them running under whatever cover is available, and definitely stop any feeding behavior until the threat is long past. Opaque shadows passing overhead have the same effect, and this includes your line or rod tip, something you should be constantly be aware of when you are presenting a fly at close range.
Finding holding water in these scenarios has some special considerations as well. While the riffled water running down the center of the channel provides visual cover from overhead predators, and is often a prime lie in bigger rivers, most of this type of water is just too thin in truly small streams to provide protection for mature fish.
Boulders midstream or in corners may have subtle overhangs that can be sidled under and should be investigated, but for the most part, undercut banks or overhanging branches and grass are the go-to lairs used by trout practicing opportunistic ambush tactics.
Typical fly presentations are generally 15 feet or less, with almost all the leader held up off the water. This allows you to get away with using slightly heavier tippet such as 4X. A hooked fish that darted out from under the bank to grab your fly will want to immediately double back to the safety of submerged roots. Using a heavier tippet for more muscle and abrasion resistance lets you stop this undesirable behavior and keep the fight out in the open.
The third physical factor that is in play is the wind. Usually considered the bane of fly fishers, on small water it can be interpreted as an advantage. On larger rivers, aquatic insects hatch across the entire width of the channel. These insects have an overwhelming amount of biomass relative to the land-based insects that end up in the water. The terrestrials that do end up in big rivers tend to be concentrated along the banks.
In tiny water, the number of insects coming from the channel is proportionally small compared to the surrounding meadow and forest insects, and for this reason, small-stream fish tend to be highly oriented toward terrestrial patterns like ants, beetles, and grasshoppers—especially in the afternoons when the wind picks up.
Trout can’t feel the wind, but I am convinced they know to look up in these conditions, a natural result of seeing events repeated on a daily basis. I can’t tell you how many times I’ve seen a nice midday mayfly hatch get blown away by a sudden increase in the wind, only to save the day by switching to something along the lines of an oversize foam ant or beetle pattern. When the hatch gets wiped out and all the other fishermen pack it in . . . that’s when the terrestrials start raining out of the trees and into the water.
I have fished some freestone streams in southern Chile that are almost devoid of any resident insect life in the channel substrate, yet they hold massive brown trout in thin water. In these places, the local Patagonian guides don’t venture out until the wind picks up in the afternoon. This is not merely a function of midnight dinners and fine wine in that part of the world. On top of having more grasshoppers than I’ve ever seen, there are huge numbers of large cicadas, locusts, and beetles of every shape and size. Accordingly, favorite patterns there trend toward things like #4-8 Amy’s Ants.
Casting problems created by wind are generally reduced in very small water. It’s rare to throw anything farther than 15 feet on a typical small stream, and it’s a simple matter to step to the other bank and get the breeze at your back if needed. When dealing with a direct downstream wind in your face, use short leaders to allow for fast turnover of bushy drys—in many cases, I am prone to cutting standard 7½-foot tapered leaders down to 6 feet or less to improve accuracy and give more fly line out the guides for energy transfer.
Also, full-flexing rods can really help loading with short presentations in the wind. Many ultralight fly rods are designed specifically for this purpose, as are most modern fiberglass rods. You can also overline your rod by two line sizes for the same effect.
Finally, while this commentary has so far referenced only dry flies or small streamers, there is definitely a time and place for nymphing on tiny water. In the absence of other structure to use for cover, fish will hold under heavier turbulences such as in plunge pools below small waterfalls, and even on small water these can sometimes be too rough to fish with conventional drys.
Scaled-down nymphing rigs are just the ticket in these frothy pockets, using downsized indicators relatively close to the fly. A single medium-size beadhead with an unweighted emerger pattern as a dropper can be very effective, and one of my favorite tactics is to use a small bicolored dubbed fur ant below the point fly. The drowned ant typically outperforms the beadhead 5 to 1. It seems ants don’t swim very well.
Small streams are great playing fields for serious fly fishers, both as training grounds and as ends in and of themselves. Today’s new wave of ultra-lightweight rods have direct application here, helping to open up miles of trout water that was previously either uninteresting or unfishable. There’s probably some small water near you, just waiting to be explored. With the proper frame of mind, I can guarantee that it will bear up to the closest inspection.
*Jonathan Wright is a freelance writer, photographer, and former fishing guide.