April Hatch Guide – Everything You Need to Know About Colorado’s Hatches in April
- brianchilbert
- 3 days ago
- 5 min read
April in Colorado is one of the most dynamic and productive months of the entire year. We’re sitting right in that pre-runoff window where flows begin to creep up, bugs are active, and trout are feeding hard. If you know what to look for and how to adjust, this can be some of the best fishing you’ll experience all season.
Let’s break down everything you need to know to dial in April on our local waters.
Blue Wing Olives (BWOs) – The Main Event
Blue wing olives are the dominant hatch in April across Colorado. These small mayflies (typically size 18–22) thrive in cloudy, cool conditions and often produce some of the most technical and rewarding fishing of the year.
How to Fish BWOs
Nymph Stage
BWOs spend the majority of their life as nymphs drifting in the current. This is your bread and butter approach, especially before and during the early part of the hatch.
Focus on:
Slow, soft seams
Tailouts and riffle transitions
Deeper buckets during lower light conditions
Fish them small, natural, and with a clean drift.
Emerger Stage
As the hatch begins (typically late morning into early afternoon), trout key in on emerging insects just below the surface. This is often when the fishing gets lights out.
Fish just under the surface
Slightly longer leaders help keep flies in the film
Dead drift is critical
Adult (Dun) Stage
Once BWOs hit the surface, you’ll see noses. This is when dry fly fishing gets technical and incredibly fun.
Look for rising fish in soft water
Match size and profile exactly
Long, light leaders are key
Cripple Stage
Cripples are often the most vulnerable stage and trout LOVE them. If fish are refusing clean duns, this is your answer.
Fish low-riding patterns
Target selective risers
Expect eats to be subtle but consistent
Top BWO Flies
Hilbert’s Daysaver Baetis (18–22)
Barr’s Emerger (18–22)
Hilbert’s Sexi Top May (18–22)
Matthew’s Sparkle Dun (18–22)
Keller’s Ms. Tickle Cripple (18–22)
Midges – Don’t Overlook Them
April is a huge month for midges, and they are often just as important as BWOs, especially on sunny days or when BWO activity is light.
What to Know
Midges hatch year-round, but April sees heavy activity
Most active from late morning through early afternoon (10 AM – 2 PM)
Found in slower water, back eddies, and softer seams
How to Fish Midges
Fish small (18–22) and precise
Double nymph rigs excel
Don’t ignore dry fly opportunities during heavy surface activity
Top Midge Flies
Hilbert’s Daysaver Midge (18–22)
Zebra Midge (18–22)
Renegade (16–20)
Caddis – Starting to Show
Toward the end of April, caddis begin to enter the picture. With our warmer-than-usual winter and spring, we’re already seeing early signs of activity.
What to Look For
Cased caddis migrating along the bottom
Sporadic adult hatches, especially in the afternoons
Increased movement in riffles and pocket water
How to Identify & Adjust
If you’re turning over rocks and seeing cased caddis, fish subsurface patterns
If you see fluttering adults or splashy rises, switch to dries or emergers
Fish tend to eat caddis aggressively compared to BWOs
Top Caddis Flies
Candy Caddis (14–18)
Guides Choice Hare’s Ear (14–18)
Graphic Caddis (14–18)
Elk Hair Caddis (14–18)
Best Attractor & “Code Cracker” Patterns
April isn’t just about matching the hatch. With changing flows and increased movement in the river, opportunistic feeding ramps up.
Stoneflies
Stoneflies become active and mobile this time of year. Trout will absolutely crush them when given the chance.
Pat’s Rubber Legs is a go-to
Fish them as your lead fly
Leeches
With rising flows, leeches get dislodged and trout key in on them as a high-calorie meal.
Mayer’s Mini Leech (olive, brown, black) is deadly
Fish slow and deep
Cranefly Larvae
This is a sleeper but a huge producer in April. As flows increase, cranefly larvae get washed into the system.
Brian Hilbert’s Philly Cheese Cranefly Larvae is a straight-up code breaker
Fish it as your anchor fly and run two smaller “hatch matching” patterns off of it.
Eggs (Spawn Season Reminder)
April is spawning season for rainbow and cutbow trout.
Important:
If you see fish in shallow water, on clean gravel, or near the bank, they are likely spawning. Please leave them alone. The future of our fisheries depends on it.
That said, loose eggs drifting in the current are a major food source.
Glo Bugs
Mylant’s Sunny Side Egg
Pegged eggs
Pro Tip:
Keep your hook 1”–1.5” from the bead and use no larger than a size 16 barbless hook to avoid injuring fish.
Streamer Fishing – Don’t Sleep on It
April is an excellent month to throw meat.
With increased flows, baitfish like sculpins, juvenile whitefish, and chubs are constantly being displaced. Big trout are on the hunt.
Our Go-To Streamers
Thin Mint
Sex Dungeon
Zoo Cougar
Barely Legal
Best Colors
Black
Olive
Rust
Yellow
Fish them on cloudy days, during flow bumps, or anytime you want to hunt big fish.
Want to Master April? Fish with a Pro
If you really want to shorten the learning curve and dial in April fishing, this is the time to get on the water with a professional.
At Colorado River Outfitters, our team of veteran guides averages 18.5 years of full-time guiding experience, and April is one of our favorite months to be on the water. Whether it’s dialing in technical BWO dry fly eats, nymphing like a machine, or hunting big fish on streamers, we’ve got it covered.
Pre-runoff is one of the best times of year for both float trips and wade trips. Fewer crowds, aggressive fish, and incredible opportunities to level up your skills.
If you’ve been thinking about booking a trip, this is your sign.
Call or text 970-236-1937 to book your trip today. Prime dates are filling fast!
Thanks for reading and we’ll see you on the water!
— The CRO Team