Fishing small streams for wild trout presents a different set of challenges than most typical fly fishing: the casts are short and the drifts are shorter, the conditions are crowded, stealth becomes a huge factor, and often a decent cast will involve throwing line across three or four separate stream features and currents, to deliver a fly within a few inches of a rock, under branches hanging just a foot or two over the water.
This type of fishing places many additional demands on an angler, but also affords him the opportunity to meet those challenges by giving him freedom in other areas. Fly selection shows this better than many other aspects of fly fishing, and a blueliner's fly box, while it may look fairly standard, is carefully tailored to this kind of fishing.
In simplest terms, there are six essential elements that make any dry fly great (or not so great) on a small stream.
This may seem like a no-brainer, but it's an extremely important feature. By saying that a small stream dry must be buoyant, I'm saying it needs to float on the water, not in it. You want your fly's body to be totally up, out of the water, seemingly bouncing across the surface.
There are a few ways to accomplish this, using foam or other buoyant synthetics, using a hollow hair like deer or elk, using a heavily greased fly, or, the most common method: tying your normal standard dry patterns with extra heavy hackling. Much like 'western-style' dries, a small stream dry benefits from a few extra turns of hackle. Flies like the Bivisible, which incorporate a lot of hackle just from the pattern are also great choices for small streams.
Also incorporated with buoyancy is making sure that the materials will accept a healthy dose of paste floatant as well. Hackle will soak up it's fair share, as will most dubbings and hair. Things like foam, quill/biot bodies, and most synthetics don't accept much floatant.
5. Water Resistancy
With all the currents and obstacles in a small stream, any dry fly is going to get dunked from time to time, regardless of how high it rides. Its resistance to the water is what will set a great fly apart from one that is more trouble than it's worth to keep it floating properly.
This property depends on two things: the way the bodies are tied and the material used. For materials, you want things that won't wick moisture into the core of the body. Things like foam, antron, or naturally water-resistant fur like muskrat or beaver. As far as method, you want a body that is wrapped or dubbed as tightly and evenly as possible. Bushy, buggy dubbing will allow the fly to soak up water through capillary action, which will eventually sink it.
4. Quick Drying
No matter how high your fly rides, or how waterproof it is, at some point (probably sooner than you think), that fly will be completely waterlogged. At this point, you'll have to dry it out again before it'll float correctly. Of course, a few good crisp false casts will wring a good deal of that water out of your fly, but after that, you've got a few options.
First, you can try any number of fly-drying products: amadou pads can squeeze a fly and absorb the moisture that comes out, powdered desiccants (like Frog's Fanny) are brush on powders that do a great job of really pulling every drop of moisture out of your fly, and recently, I've started seeing a few 'spray-on' drying agents, that come in a pump bottle.
All of these products work, to an extent (I carry powdered desiccant and have been trying a few spray-ons as well). Try the false cast until it doesn't work, as its the fastest method, then after that, I usually dust it with Frog's Fanny, false cast it again to knock excess powder off, then spray a shot or two of a liquid dryer/waterproofer on, and false cast again a few times, then reapply my paste floatant.
Eventually, however, the water will work its way down to the thread and the insides of your fly, and no amount of false casting or chemical will revive it. At this point, clip it off, hang it on your fly patch, and let it air dry, while you tie on a fresh one. Naturally, it's a good idea to have several copies of each of your best patterns.
Another great reason to have multiples of your best flies is because if you're on a small stream, you're bound to surrender a few flies (or a lot of flies) to trees, rocks, bushes, fallen logs, and whatever else happens to be close at hand. The ones you do manage to recover often are a little worse for the experience, with messed up wings, twisted hackle, and crinkled hair.
On a good day of fishing, the fish themselves will shred a fly to bits, too, and a well-chewed fly is a thing of beauty.
The best way to delay the inevitable is to concentrate on tight ties at the bench. Practice technique, use minimal thread, use a drop of head cement if necessary (but if your technique is good enough, you shouldn't need it). In short: you want bulletproof flies when you start out. There's nothing you can do to increase the durability of a fly once you're on the water.
I know I said up above that a buggy-dubbed fly would absorb water. That's true, it will, but there's other ways to get that look that won't turn your fly into a sponge. Hair wings, heavy palmered hackle, and materials like peacock herl that will break up the outline of your fly are all safe bets.
The reason for this is because you want to be able to minimalize your fly selection while making sure you're covered for most situations. In this way, you can tie an elk hair caddis in light tan, olive, medium brown, and black...all in a size #14, and be covered for tan caddis, early stoneflies, mosquitoes, BWOs, and olive caddis.
When you're on a small stream, it's usually good to dumb down your entomology skills, and instead of thinking in terms of 'isonychia', 'october caddis', and 'baetis', start thinking in terms of 'little', 'big', 'light', and 'dark'.
The most important aspect of a small stream dry fly is that it is visible. To you, not the fish. The fish will be able to see any fly, no problem, but in the twisting, tumbling currents of a mountain stream, it's easy to lose track of your fly. You want to make sure that you're looking at the fly when that brookie rises to it.
In this vise, this means light colors and bright colors. For any hair wings, I use bleached elk or deer. In other flies, you can use antron yarn in fluorescent green, pink, and orange, as well as brightly colored foam. For parachutes, both bright and bleached white turkey flats and calf body hair are used with great results as well.