Colorado fly fishing doesn't have an "off season" — it has four completely different seasons, each with its own hatches, water conditions, and strategies. The angler who shows up with summer tactics in January is going to have a long, cold, fishless day. Here's what to expect and how to plan around it.
Winter (December – February)
Winter fishing in Colorado is real, and it can be excellent — if you adjust your expectations. Fish are sluggish in cold water. They won't chase anything. Your presentations need to be slow, precise, and close to the bottom.
What's hatching: Midges. That's basically it. Blue-winged olives (BWOs) will make occasional appearances on warm, overcast afternoons in December and February, but midges are the workhorse hatch from November through March. Sizes 20–24, which means small flies and light tippet.
Where to go: Tailwaters are your best bet. The water below dams (Blue River, Fryingpan, South Platte below Cheesman) stays at a relatively constant temperature through winter — cold but not frozen. Freestone rivers can fish, but ice shelves, anchor ice, and access problems make them less reliable.
Peak window: Fish the warmest part of the day — 11 AM to 3 PM. Midge hatches often peak around noon to 1 PM. There's no reason to be on the water at dawn in January unless you enjoy suffering. The fish aren't moving early either.
Gear considerations: Layer for immersion, not air temp. Neoprene gloves (fingerless or flip-mitt), hand warmers, and insulated wading boots make the difference between a productive day and a miserable one. Bring a thermos.
Spring (March – May)
Spring is the transition season — and the trickiest to plan around. Early spring (March) fishes like late winter: midges and BWOs on tailwaters. But by mid-April, things start to change fast.
The runoff problem: As temperatures warm and snowpack begins to melt, rivers start rising. By late April or May, most freestone rivers are entering runoff — flows doubling or tripling, water turning brown and opaque. This is the worst time to fish freestone rivers. The water is too fast, too dirty, and too dangerous to wade.
What's hatching: BWOs become more consistent through March and April. Caddis start showing up in April on lower-elevation waters. Stoneflies begin their migration to shore in May. But on blown-out rivers, it doesn't matter what's hatching — the fish can't see it.
Runoff timing varies wildly. A low-snowpack year might see runoff start and end in April. A big snow year can push peak runoff into July. Check the live conditions daily during spring — rivers change fast.
Where to go: Stick to tailwaters through runoff. The Blue River, Fryingpan, and South Platte below Cheesman all maintain fishable flows when the freestones are blown. Also consider high-altitude lakes — ice-off usually happens in May and the early open-water fishing can be spectacular.
Summer (June – August)
Summer is prime time — but the window opens at different times depending on the water. Rivers coming off runoff clear up gradually: lower-elevation sections first, high-altitude streams last. A river might be fishable in the canyon while still blown out at the headwaters.
What's hatching: Everything. June brings the tail end of the stonefly migration and the beginning of PMD (Pale Morning Dun) hatches. July is peak dry fly season — PMDs, caddis, Yellow Sallies, and the legendary Green Drakes on specific waters. August shifts to terrestrials (hoppers, ants, beetles) as the big mayfly hatches wind down. Tricos appear on many rivers in August, providing incredible morning dry fly fishing for those willing to fish size 22 flies.
Where to go: Everywhere. By mid-July, most Colorado rivers are fishable. The freestone rivers that were dangerous in May are now at prime levels. The Arkansas through Brown's Canyon, the Eagle River, the Roaring Fork, the Colorado through Glenwood — these are all summer rivers that fish best June through September.
The hopper-dropper rig: In July and August, a foam hopper pattern with a bead-head nymph dropped 18 inches below it is the most productive setup on most Colorado rivers. The hopper acts as both a strike indicator and a meal. Fish eat the hopper about 30% of the time and the nymph about 70%.
Summer hazards: Afternoon thunderstorms are almost daily in the Colorado mountains from July through mid-August. Plan to be off the water by 2 PM or watch the sky carefully. Lightning is the #1 weather-related killer in Colorado. Also: flows can spike 30–60 minutes after a heavy upstream storm even if it's sunny where you're standing.
Fall (September – November)
Fall is arguably the best season for fly fishing in Colorado. The crowds thin out after Labor Day. The hatches are still active. The fish are feeding aggressively to build reserves before winter. And the flows are at their lowest and most stable of the year.
What's hatching: BWOs make a major comeback — fall BWO hatches on overcast days can be the most prolific dry fly events of the year. Tricos continue through September. Midges become increasingly important as temperatures drop. By November, you're back to a midge and BWO game.
The spawn: Brown trout spawn in October and November. Spawning fish are on redds (gravel nests) in shallow water. Some anglers target spawning fish, but many consider it unethical — the fish are vulnerable and stressed. If you see fish actively on redds (paired up over clean gravel, fanning with their tails), give them space.
Fall fishing tip: The best fall days are overcast and cool — high 40s to low 50s with cloud cover. These conditions trigger the strongest BWO hatches. Bluebird days in fall look beautiful but fish poorly. Welcome the grey.
Where to go: Everywhere is good in fall. The South Platte tailwaters are legendary for fall BWO fishing. The Fryingpan's "midge factory" section below Ruedi starts its peak season. Freestone rivers like the Eagle and Roaring Fork are at low, clear flows perfect for sight-fishing.
Planning Around the Calendar
The Hatch Calendar on this site shows what's hatching on each Colorado river by month — fly patterns, sizes, and technique notes. Use it to plan trips around the hatches you want to target. Cross-reference it with the live conditions to confirm the river is actually fishable before you make the drive.
The best approach for beginners: pick one or two rivers per season, learn them well, and let the data tell you when to go. A river you know intimately at 250 CFS will always outfish a new river you're guessing at.
Plan your next trip by season.