The Starting Lineup – 3 Flies You MUST Have for August
- brianchilbert
- 1 day ago
- 6 min read
August in Colorado is one of the most underrated months of the entire fly fishing season. Yes, we’ve battled warm water, low flows, and changing conditions throughout much of the summer. But things are finally beginning to trend in the right direction. Cooler nights, scattered afternoon rains, and strategic reservoir releases have improved water temperatures on many of our favorite fisheries. The trout are responding exactly how we’d hoped, they’re feeding aggressively whenever conditions allow.
One thing that makes August unique is just how many food sources are available to trout at the same time. Stoneflies are still present. Baetis begin to become more important. Midges never leave. Tricos are hatching. Caddis remain a major player. Terrestrials are everywhere, and fluctuating water levels continue to wash worms and larger nymphs into the drift.
Rather than carrying dozens of fly boxes to the river, here’s the exact starting lineup the Colorado River Outfitters guide team has been leaning on this month.
If these flies are in your box, you’ll have confidence no matter where your day takes you.
1. Half Back Nymph
Size 10
If we had to pick one anchor fly for August, this would probably be it. The Half Back Nymph has been around forever, and for good reason, it simply catches fish.
With the fluctuating flows we’ve experienced recently, stonefly nymphs are constantly getting knocked loose from the rocks. Every time flows increase from rain events, tributary inflows, or dam releases, trout know there’s a buffet floating downstream. They slide into feeding lanes looking for larger, calorie-rich meals.
That’s exactly where the Half Back shines.
Its buggy profile and natural movement imitate dislodged stonefly nymphs perfectly, making it an outstanding lead fly in virtually any two-fly nymph rig.
At Colorado River Outfitters, we’re fishing this pattern primarily as our anchor fly. It gets your rig down quickly while also producing plenty of eats on its own. Then we’ll trail the next two flies behind it.
Whether you’re fishing the Roaring Fork, Colorado River, Fryingpan, or Eagle, this fly deserves a permanent place in your August rotation.
Why we love it:
Excellent anchor fly
Perfect stonefly imitation
Gets your rig deep quickly
Produces quality fish throughout the day
Works especially well after flow increases
Pro Tip from Brian Hilbert
“Don’t overthink your anchor fly. August trout are opportunistic feeders. If flows have bumped overnight, start with a Half Back before experimenting with anything else. Cover water confidently and let the smaller trailer flies match whatever hatch is occurring behind it.”
2. San Juan Worm
Size 14
Every angler knows the San Juan Worm catches fish.
The secret is knowing when to fish it.
This month has been a textbook example.
Recent rains have bumped flows on the Eagle and Colorado Rivers while increased releases have freshened up portions of the Roaring Fork. Those changing water levels wash earthworms and aquatic worms into the current, creating one of the easiest meals trout will see all day.
Fish recognize this immediately.
Whenever you arrive at the river, make checking the streamflow part of your routine.
If the gauge shows the river has risen, even slightly from rainfall or tributary inflows, don’t hesitate.
Tie on a worm.
Many anglers avoid worms because they aren’t glamorous. Guides don’t care about glamorous, we care about effective.
The San Juan Worm consistently puts fish in the net during changing water conditions because it represents exactly what trout expect to see after higher water.
We often pair it behind the Half Back Nymph, creating one of the most productive August combinations we’ve fished this season.
Why it belongs in your August box:
Deadly after rain events
Excellent during fluctuating flows
Natural food source trout actively seek
Simple presentation
Great confidence fly for all skill levels
3. Sexi Top May – Chocolate
Sizes 18–22
If there is one fly that has been the work horse this August, it’s the brand-new Chocolate Sexi Top May.
This new color from Montana Fly Company has quickly become a staple in our guide boxes.
Designed by Brian Hilbert as part of the popular Sexi Top series, the chocolate body paired with the bright white wing creates an incredibly versatile emerging insect profile.
That’s important because August hatches are rarely simple.
It’s common to see:
Baetis
Midges
Tricos
Small Caddis
Miscellaneous emerging insects
All occurring during similar windows. Instead of changing flies every fifteen minutes trying to perfectly “match the hatch,” the Chocolate Sexi Top simply imitates emerging life.
That’s why it has become our workhorse.
We’ve especially been impressed with the size 22, which has fooled selective trout throughout the Roaring Fork and Colorado River during late morning hatch windows.
If you enjoy technical fishing but don’t enjoy changing flies every few minutes, this pattern deserves serious attention.
Why we love it:
Matches multiple insect species
Outstanding emerger profile
Excellent during mixed hatches
Perfect trailer fly behind a larger anchor
Especially productive in size 20-22
Pro Tip from Matt Fletcher
“Don’t get locked into fishing one hatch. August often brings overlapping insect activity. Instead of trying to perfectly identify every bug you see, fish confidence patterns that imitate emerging life. The Chocolate Sexi Top has become one of those flies that simply keeps producing when several different insects are active.”
Bonus Fly:
Elk Hair Caddis
Tan – Sizes 14–18
If you’re willing to get up early, you’ll be rewarded.
Morning dry fly fishing has been exceptional.
Most of Colorado’s caddis species perform their mating flights overnight. By sunrise, countless spent adults and egg-laying females end up drifting naturally along the surface.
The trout know it.
Some of our best dry fly fishing this month has happened during the first few hours of daylight, especially on the Colorado River.
The CRO guide team prefers fishing tan Elk Hair Caddis patterns in sizes 14–18 depending on the river and hatch density.
Presentation matters.
Instead of firing casts into the deepest pools, focus on:
Skinny riffles
Shallow banks
Pocket water
Soft seams beside faster current
These are exactly the places trout slide into to intercept helpless adult caddis.
Sometimes the best dry fly fishing of the day is over before most anglers have even parked their truck.
Current Fishing Conditions Continue to Improve
If you’ve been waiting for conditions to improve before planning your trip, now is an excellent time.
Many of our fisheries have benefited from:
Cooler overnight temperatures
Recent rainfall
Improved water temperatures
Increased tributary inflows
Strong aquatic insect activity
While we continue encouraging anglers to carry thermometers and practice ethical fishing during warmer afternoons, the rivers currently within safe temperature windows have been producing outstanding fishing.
Our guides have enjoyed some incredible days recently, with healthy trout feeding aggressively on both nymphs and dry flies.
Check Out Our Latest Fishing Report
Want the most up-to-date river conditions before you head out? Be sure to read our latest Colorado fishing report, where we cover:
Current river flows
Water temperatures
Closures and regulations
Best flies by river
Guide observations from the past week
What we expect over the coming days
Fish With Colorado River Outfitters
Reading about the fishing is one thing. Experiencing it with a professional guide is another.
At Colorado River Outfitters, our guides spend more days on these rivers than just about anyone. Every trip is built around current conditions, water temperatures, insect activity, and where fish are actively feeding, not where they were last week.
Whether you’re a first-time fly angler or an experienced trout hunter looking to sharpen your skills, we’ll provide everything you need for a memorable day on the water.
From premium equipment and custom fly selections to local knowledge gained through hundreds of guide trips every season, our goal is simple:
Help you become a better angler while putting you on fish.
Water conditions are improving, trout are feeding hard, and August is shaping up to be one of the better late-summer windows we’ve seen.
We’d love to show you why.
Final Thoughts
You don’t need fifty different fly patterns to be successful this month.
Start with these proven producers:
Half Back Nymph (#10) – Your go-to anchor fly.
San Juan Worm (#14) – Essential after rain or rising flows.
Chocolate Sexi Top May (#18–22) – The ultimate do-it-all emerger for August hatches.
Bonus: Tan Elk Hair Caddis (#14–18) – A must-have for early morning dry fly fishing.
Stock your box, hit the river early, pay attention to changing conditions, and don’t overlook the simple patterns that continue to outperform year after year.
We’ll see you on the water.
-The CRO Team
Want to meet the team behind this Intel?
Meet our team of veteran fly fitting guides here:
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