Spey is one of the older styles of fly fishing, having origins in the British Isles, and specifically, Scotland, where it was developed to target Atlantic Salmon. The Spey cast itself -- an aerial combination of a figure-eight and a roll cast -- is something that I don't personally claim to execute well, but its utility and effectiveness are unquestionable. For large rivers without defined structure to target as holding and feeding lies, or for migratory fish like salmon that aren't really inclined to that behavior anyway, Spey presentation and gear can cover large sections of moving water like no other fly fishing technique. First developed with fixed lines attached to the tips of wooden "Greenheart" rods of eighteen feet or more that required two hands to manipulate, the Spey cast may well predate the invention of the functional fly reel.
The other component of Spey technique is the downstream, swung presentation of the fly, sweeping across wide swaths in a search for quarry. Many times, fish can be provoked to move several yards or more to hammer a moving underwater fly, and the strikes are generally violent, providing instant feedback for the angler that modern nymph fishing lacks. The experience rivals dry-fly fishing for aesthetics and adrenaline factor, with enthusiasts typically being extremely firm in their convictions.
Salmon and trout are both members of the family Salmonidae, with the former being genetically programmed for spawning migrations between fresh and salt water, and the latter generally considered to be landlocked adaptations of their original oceangoing forms. There are exceptions in both directions. Salmon fresh in from the ocean are considered "bright", and display much more vigor than fish that have endured migrations of hundreds or even thousands of miles to reach breeding grounds. By definition, rivers close to the sea are of generally larger volume -- being fed by numerous upstream tributaries -- and can also be flatter, with less in the way of large boulders and bends to create places for fish to hang out in. Spey presentations are well suited to these conditions.
For those of us who don't live near classic coastal salmon water, the Spey technique still has application. Trout are also inclined to much of the aggression of salmon and steelhead, chasing down flies tracking under the surface through their neighborhoods. Many times, emergent insects such as Caddis display behavior that a swung fly mimics perfectly, with the imitation darting through current seams while fluttering feather materials give the appearance of unfurling wings and shedding exoskeleton casings. The secret lies in mending the line at the correct time during the swing, causing the soft materials of the fly to "breathe", and giving the appearance of life. Allowing the fly to drag in strong current causes the materials to collapse against the hook body, and all is lost. It's very much a touch thing, as is the angler's strike, which is restrained and delayed relative to the typically vicious takes.
I myself have been a fan of swung soft hackles ever since Rod Patch at Ark Anglers in Salida, Colorado turned me on to the concept in the very early 2000's. Rod was an early inland dealer of weighted poly leader systems that allowed light flies with fluffy hackle materials to be presented at depth on the typically steep water of the southern Rockies with standard single handed trout rods. Mending was a snap, allowing the floating fly line to be repositioned on the water while the soft lead or tungsten based coatings on the poly leader knifed though the water, carrying the flies down deep. This was a revelation to me, and without having to carry a second sink tip line, I proceeded to clean up using a downstream presentation with simple traditional partridge hackled "spider-type" patterns all over Colorado.
Fast forward eighteen years, and the visionary design minds of the manufacturing sector have been vigorously pursuing the whole concept of swung spey tactics being applied to trout. Modern carbon fiber salmon and steelhead gear is on the large side of things for fly fishing equipment, with rods of up to 14' that can cast #10 weight lines being used for heavy species like Chinook. The relatively new category of "Micro Spey" gear scales things down for both fish and playing field. Design forward rod makers such as Tim Rajeff's Echo brand now offer two-handed models in the 11' range with line weights down to #3 that are coveted among the cognoscenti. The extra length of these rods allows for continuous drift and mending control in big water that is much more difficult with shorter sticks. Line manufacturers have been quick to jump in as well, offering precise designs to match both the rods being marketed and the conditions at hand. The diversity and selection of lines and sinking heads available is truly mind-boggling, and allows the angler to tailor his setups for both water and personal taste.
While traditional wet flies for trout have always been widely available commercially, a feedback loop of innovation in fly design exists alongside the long rod movement, with social media communities of Micro Spey enthusiasts now conjuring up patterns specifically tailored for the exercise. Tyers online regularly post images showing miniature versions of perfectly executed patterns that would not be out of place in a coffee table book on British Columbian Steelhead. The difference is, these wet flies are not being tied on size #1/0 and #2 up-eye hooks, but on #10s and #12's -- and sometimes, much, much smaller. Elegant spun Deer-hair patterns designed to be skated crosscurrent "damp" in the surface film are in evidence, as are heavily weighted flies substituting short haired pine squirrel for the bulkier rabbit found on popular Bunny patterns .
Other flies that employ materials normally found in trout streamer patterns are on display, such as bucktail, but with typically lighter dressing executions -- again, allowing for materials to move in the water in addition to just providing a meaty profile. It should also be mentioned that there are photos being posted of some VERY solid fish being caught on the swing. Other species of fish are not beyond the scope of attention, either, with the Smallmouth Bass river contingent making itself known.
Trout fishing is a many faceted thing, and there seem to be as many ways to approach it as there are fish in the river. Micro Spey opens up new territory in many respects, and freshens up options for fly fishermen operating on otherwise difficult terrain or just for those looking to change things up and enjoy a different and deadly way to fish.