The Trico spinner fall is the only hatch on this site where the fly is smaller than the eye of most hooks people learned to tie on. Tricorythodes, the genus behind the name, is a mayfly of size 20 to 26 with a black body and clear wings, and from July into September it comes back to the water by the thousands every morning on twenty of the rivers listed here. Trout line up in the slow tailouts and eat spinners with a rhythm you can count, and the fishing is as technical as anything in freshwater: fine tippet, exact timing, one fly among a hundred naturals, and fish that have been doing this every morning for weeks.
A tiny mayfly with an unusual schedule
Tricorythodes belongs to the family Leptohyphidae. The nymphs are small crawlers that live in silt and weed in slow water, which is why the hatch is strongest on tailwaters and spring creeks rather than pocket-water freestones. What makes the Trico strange is the timing. Male duns hatch overnight and in the early morning; female duns hatch after dawn. Both molt into spinners within an hour or two, which is fast for a mayfly, and then the mating swarm forms over the riffles in mid-morning, when the air warms enough. The spinners fall to the water spent, and that is the event trout wait for. On a typical summer day the spinner fall is a mid-morning affair, and it comes later on cool mornings and earlier on hot ones.
The dun hatch is fishable if you are on the water at first light, but the spinner fall is where the numbers are, and the female spinner, black body with a pale olive or cream abdomen, is the imitation to carry. The male spinner is black throughout.
Where the Tricos are on this site, and when
The peak months in the river matrices cluster tightly:
- July through September: the Missouri, the Bighorn, and Silver Creek. These are the longest Trico seasons here, and the Missouri and Bighorn spinner falls are the ones people travel for.
- August and September: the Madison and the Henry's Fork, both listed "on" through October.
- July and August: the Colorado tailwaters, the Frying Pan, Blue, Taylor, Gunnison, and South Platte, plus the Arkansas; the Provo and Middle Provo in Utah; the San Juan; Hat Creek and the Owens in California; the Boise and Teton; and the Yakima.
- Lees Ferry lists Tricos as "on" in July and August without a peak, a minor event on that river compared to its midges.
Notice what is on the list: tailwaters and spring creeks almost exclusively. The Madison and Yakima are the only freestones, and the Madison's Tricos are on the slower water below Ennis, not in the wade stretch.
Patterns from the river pages
Every Trico river on the site lists a Trico Spinner in 22 to 24, and several go to 26: the Frying Pan, Hat Creek, Henry's Fork, Provo, San Juan, Silver Creek, and South Platte. The second fly is almost always a CDC Trico in 22 to 24, which is a dun or emerger with a CDC wing that floats well and is easier to see. The Bighorn, Henry's Fork, Lees Ferry, San Juan, and Taylor add a Parachute Trico with a white post, and the Missouri and Silver Creek list a Poly Trico spinner with polypropylene wings that stay flat in the film. Buy the spinners in both 22 and 24, because the females run a size larger than the males and the fish sometimes prefer one.
Fishing the spinner fall
The problem is not fooling the fish. It is getting your one fly noticed among the naturals and setting the hook when it is taken. Some things that help:
- Pick one fish. Casting at a pod is casting at nothing. Find a steady riser, learn its rhythm, and time the cast so the fly arrives as it is coming up.
- Get above and across. A downstream reach cast with slack lets the fly reach the fish before the leader does, which matters on 7X in flat water.
- Two flies. Fish a size 22 spinner a foot behind a Parachute Trico or a small visible dry. The front fly is the sighter; when a fish rises within a foot of it, set.
- A cluster pattern. When spinners are so thick the fish are gulping, a size 18 or 20 fly with two or three spinners tied on one hook gets picked out because it is bigger.
- Set softly. Lift the rod, do not strike. A size 24 hook on 7X breaks on a hard set, and the tiny gap seats better with a gentle pull anyway.
- Stay after the fall. Trout keep eating drowned spinners for an hour after the last ones hit the water. A spinner fished a few inches under the surface, or a black size 22 nymph, catches those fish.
Reading the morning
Arrive before the swarm. If you get to the Missouri or the Bighorn at nine and the spinners are already on the water, you have lost the chance to find the best fish while it is still feeding on duns and has not yet locked into the spinner rhythm. Look for the swarm forming over the riffles: a shimmering column of insects a few feet above the water, rising and falling. When it starts to drop, move to the tailout or the slow inside seam below that riffle, because that is where the spent spinners will collect and where the fish will be. Wind delays the swarm and can blow it into the bank, where the fall concentrates against the grass; on a breezy morning fish the downwind edge.
Gear and tippet
A 9-foot 4-weight or 5-weight, a 12-foot leader tapered to 6X, and a spool of 7X for the flattest water. Nylon rather than fluorocarbon for the dry, because it floats. Fly floatant on the leader butt, not on the tippet. A small net, because you will be landing fish on tippet that breaks under two pounds of pull. Most of the Trico rivers above are special-regulation water, so check the state fish and game agency for the section you are fishing before you go. And bring a PMD box for the afternoon, because on the Missouri, Bighorn, and Frying Pan the PMDs are peaking in the same months and take over once the Trico fish stop.