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Fall in Colorado is a tricky, beautiful beast. Days cool, bugs change, fish start thinking about winter (or spawning), and what worked in summer might get stared at suspiciously. But the trout are still eating. You just need to pick flies that match what they want now. I combed several recent guides [Orvis, local blogs, pattern compendiums] and found solid consensus – plus a few under-the-radar gems. Here are ten flies to load in your box, why they work, and when to throw them.
Top 10 Flies for Fall Fly Fishing in Colorado
1. RS2 / Sparkle Wing Baetis
Description: A tiny emerger pattern that imitates blue-winged olives, one of the most consistent fall hatches in Colorado.
Why Fall Trout Love It: BWOs are a staple in cool, overcast conditions. Trout key in on these emergers when the bugs are stuck in the surface film.
Best Conditions: Cloudy mornings and afternoons, slower seams, and riffle edges.
Presentation Tips: Long 12–14’ leaders with 5X–6X tippet. Dead-drift just under the surface, or let it swing gently at the end of a drift.
2. Parachute Adams
Description: The universal mayfly imposter — versatile, visible, and reliable.
Why Fall Trout Love It: It passes as a dun, midge, or spinner depending on how it rides, making it a problem-solver when trout are picky.
Best Conditions: Clear skies or mixed hatches, especially in riffles and tailouts.
Presentation Tips: Fish in sizes 14–20. Focus on drag-free drifts.
3. Elk Hair Caddis
Description: A buoyant dry fly that matches October caddis and other lingering caddis species.
Why Fall Trout Love It: Caddis remain active late into fall, especially around fast water. The elk hair wing makes it easy to spot and hard for trout to ignore.
Best Conditions: Choppier riffles, overcast afternoons, or as a dry-dropper anchor.
Presentation Tips: Use size 14–18. Pair with a small bead-head dropper for bonus hookups.
4. Soft Hackle BWO Emerger
Description: A wet fly with soft hackle that pulses like an emerging insect.
Why Fall Trout Love It: In cold water, trout love half-drowned emergers — easy meals they don’t have to chase.
Best Conditions: During or just after BWO hatches in slower pools and seams.
Presentation Tips: Swing them across current seams or fish subsurface on a greased leader.
5. Drowned Ant
Description: A sunk terrestrial pattern imitating ants swept into the current.
Why Fall Trout Love It: September winds and cooler nights knock terrestrials into the water, and trout opportunistically snack on them.
Best Conditions: Near banks, under willows, and after windy afternoons.
Presentation Tips: Fish unweighted near the surface or let it sink naturally under light tippet.
6. Egg Pattern (Glo-Bug / Flashtail Egg)
Description: Bright, simple yarn flies imitating trout eggs.
Why Fall Trout Love It: Browns and brookies spawn in fall. Opportunistic trout downstream gorge on loose eggs.
Best Conditions: Just below redds or in deeper runs during spawn season.
Presentation Tips: Use in tandem with a nymph. Dead-drift along the bottom with enough weight to stay down.
7. Spent Spinner / Cripple Patterns
Description: Flies imitating dying or spent adult mayflies lying flat on the water.
Why Fall Trout Love It: Trout prefer easy, motionless meals during cooler months.
Best Conditions: After a hatch has finished, usually late afternoon or early evening.
Presentation Tips: Grease your leader for delicate drifts in foam lines.
8. Streamer (Woolly Bugger / Mini Leech)
Description: Big, meaty flies imitating minnows, sculpins, or leeches.
Why Fall Trout Love It: Shorter days and colder nights push trout to bulk up on high-calorie meals.
Best Conditions: Overcast days, dawn/dusk, or in stained water.
Presentation Tips: Strip in varied speeds, or swing through deeper runs. Dark colors (olive, black) excel in low light.
9. Hare’s Ear Nymph
Description: A buggy, tan-brown nymph that can imitate nearly anything — mayflies, caddis larvae, or stonefly nymphs.
Why Fall Trout Love It: In clear fall flows, trout keep feeding on subsurface insects. This fly matches a broad menu.
Best Conditions: Midday, when surface activity is low.
Presentation Tips: Dead-drift deep under an indicator with small split shot. Sizes 14–18 work best.
10. Yellow Sally / Attractor Dry
Description: A bright, high-riding dry fly pattern that gets noticed.
Why Fall Trout Love It: When hatches are thin, trout still take curiosity strikes at something flashy.
Best Conditions: Sunny afternoons or in lightly stained water.
Presentation Tips: Fish in sizes 12–16. Give a subtle twitch to wake up lethargic trout.
Common Threads: Why These Flies Rank
From going through at least three of the top guides/blogs in Colorado, here are the repeating reasons certain flies are chosen — and what that says about the fall fishing game.
Emerger/BWO / Midge dominance
As summer bugs fade, smaller insects like BWOs, midges, and emergers become staples. Fish become more selective. Smaller, subtler flies are required. It’s nearly always present in every guide.
Versatility & “visible enough” patterns
Flies that can be fished as emergers, waters that have variable clarity, times when light is low (morning, overcast) need flies that are visible without being huge. Parachute wings, foam, hackles help. Also, flies that cover multiple insects help (e.g. something that could be a dun or midge).
Feed-up behavior
Trout in fall are prepping for winter (or spawning). That means more aggressive feeding, including going after terrestrials, eggs, streamers, anything that looks high-calorie. So guides always include streamers, egg patterns, terrestrials.
Water & light changes
Cooler temps, lower flows, clearer water, shorter daylight, rising and setting sun angles all affect bug behavior (and trout behavior). Fly choice needs to adapt: smaller flies, lighter leaders, careful presentation. Many guides stress fishing early/late, covering water, being stealthy.
Matching what is there (but being ready when it's not obvious)
If you see BWOs or emergers, match them. But if bugs are sparse, bring out attractors, streamers, bigger profile flies. Having a fly box with a range is commonly recommended.
Putting It Together: How I Fish Fall in Colorado (My Modestly Successful Routine)
Here’s how I try to use those flies & patterns on an average fall week (i.e. crisp mornings, warming mid-day, maybe cloudy, maybe some wind, water cooling):
- Start early: morning light is low, BWOs/emergers often active just off riffles. I’ll throw RS2 / Sparkle Wing Baetis under an indicator or as a emerger, or fish a Parachute Adams / soft hackle emergers depending on flow.
- Mid-morning to midday: if banks have overhanging trees, try a drowned ant or hop up to terrestrials if any bugs are falling. If water clarity drops (runoff or leaves falling), go with streamers or egg patterns near structure.
- Afternoon / evening: look for surface action – spent spinners, BWOs. Also streamers near dusk, when trout seem more willing to chase.
- When water is cold (< ~55-60°F) or flows drop: more weighted nymphs (Hare’s Ear, or bead heads), shorter leaders, lighter presentations.
- Always adjust fly size / color: olive/gray/dun tones in most cases; hints of orange or yellow for attractors. If water gets dirty or light is low, dark flies show better; clean clear water calls for subtle tones.
Final Thoughts
If there’s a takeaway (beyond “bring more flies than you think you need”), it’s this: fall is about choices — small bugs, emergers, and subtle hatches plus occasional big meals. Fly boxes that lean too heavily one way or the other (all dries, no streamers; all small flies, no terrestrials or eggs) are going to miss out. Fish are smart, light is weird, water is changing.
So load up, keep your eyes open (for bugs, for surface texture, for currents), and don’t be too proud to switch flies. Sometimes the trout just want something loud, and sometimes they want the tiny thing barely moving.
