Pale Morning Dun Hatch Colorado: Your Guide to PMD Season

The Hatch That Rearranges Your Calendar

The first time I watched a pale morning dun hatch blow up on the Frying Pan flats, I nearly forgot to cast. Tiny pale-winged mayflies poured off the water like confetti, and every trout in the run abandoned whatever they had been eating to line up and sip. I missed my first three fish because I was still rigged with a size-12 stonefly nymph from the morning. By the time I knotted on a size-18 comparadun, I had learned the lesson every Colorado dry-fly angler eventually learns: when PMDs show up, nothing else matters.

The pale morning dun hatch Colorado season is the event that transforms tailwater slicks into all-day dry-fly water. From late May through mid-August, these pastel mayflies move upstream through the state’s best rivers, and if you understand the timing and life stages, you can follow the wave for weeks. Here is everything you need to fish it well.

When and Where: River-by-River Timing

Colorado’s PMD season starts on the lower-elevation tailwaters and climbs toward the high country over about eight weeks. The table below covers the core windows, but keep in mind that water temperature is the real trigger. Once a tailwater consistently holds 54-58 degrees through midday, start watching for wings on the surface.

Tailwater Windows

Freestone and Meadow Windows

Colorado tailwater PMDs generally kick off two weeks earlier than freestone hatches, so you can fish your way west and uphill as the season builds. Check Colorado Parks and Wildlife fishing regulations for any gear-specific rules on your target water before you head out.

Before committing to a drive, pull up River Conditions in the FlyGuysNLies app — if the Frying Pan’s water temp is still sitting at 48°F by 10 a.m., the PMDs are sleeping in too. The app’s Hatch Charts also track PMD emergence intensity river-by-river, so you can see whether this week’s window is peaking on the Gunnison or still two weeks out on the South Platte.

Understanding the Life Stages

Success during a PMD hatch comes down to matching the life stage trout are keyed on at that moment. The nymphs are clingers and crawlers that live along riffle edges and gravel bars, typically with dark olive or brown bodies. As water warms through midmorning, they begin migrating toward the surface, and that transition zone — from streambed to film — is where the fishing often starts.

Emergers are the stage that drives trout crazy. PMD nymphs rise slowly, often hanging just below or trapped in the surface film, making them easy targets. A CDC soft hackle or cripple pattern fished in the film can be devastating during this phase. Once the duns pop through and ride the current drying their wings, you are into classic dry-fly territory. Sunny days push duns off the water quickly, but cloudy afternoons can keep them floating for long stretches, extending the prime window.

Do not overlook the spinner fall. Spent-wing PMD spinners hit the water at dawn and again at dusk, and trout feed on them with the kind of quiet, rhythmic rises that are easy to miss if you are not looking. Arrive 45 minutes before sunrise, position downstream of likely feeders, and fish a rusty spinner on 6X with a slack-line cast.

The Daily Rhythm

A PMD day has a predictable arc. At sunrise, spinner falls from the previous evening’s mating flight collect in eddies and tailouts — fish them on 6X before the light gets harsh. From about 8 to 10 a.m., nymphs stage in the gravel, and a two-nymph rig bounced through riffles at 1.5 times the water depth picks up fish that have not started looking up yet.

The magic window opens between 10 a.m. and early afternoon when emergers break through the film and duns begin riding the current. Rig a dry-dropper — comparadun or film critic on top, Barr’s Emerger dangling 18 inches below on 5X. As refusals pile up, drop to 6X and switch to a cripple. On overcast days the hatch can roll straight through until the evening spinner return around 7 or 8 p.m.

Fly Patterns That Earn Their Keep

You do not need three dozen PMD patterns, but you do need the right ones across all four life stages. Here is what should be in the box:

• Dries: Comparadun PMD (#16-20) for slicks, Film Critic PMD (#16-18) for its half-submerged profile on tailwaters, and a parachute variant for choppier freestone riffles
• Emergers: Barr’s Emerger PMD (#16-18) is the South Platte staple, Crippled PMD (#16-18) with a trailing shuck for picky fish, and a PMD Soft Hackle (partridge and olive, #16-18) to swing through seams during early emergence
• Nymphs: Pheasant Tail PMD (#16-18) with a pink thorax thread, Two-Bit Hooker PMD (#16) with double tungsten for deep buckets, and a Split Case PMD (#18) for the Frying Pan flats
• Spinners: Rusty Spinner PMD (#16-18) for dawn and dusk, Spent Wing PMD (#18-20) with CDC wings for high-country meadow sippers

Color matters more than most anglers realize. Early-season PMDs on cooler tailwater riffles tend toward olive-brown in size 16. By mid-season on bright days, the bugs lighten to pale yellow in size 18. High-country creeks produce a sulphur-tan variant, and spinners shift to rusty orange. Carry at least two body shades and swap at the first refusal.

River Playbooks

South Platte Tailwaters. Start the morning nymphing the deep runs at Cheesman with a Two-Bit Hooker and Split Case rig set four to five feet deep. As risers appear late morning, transition to a Barr’s Emerger under a comparadun dry-dropper. By afternoon, the Film Critic fished on a downstream reach cast with a drag-free drift is hard to beat. Spinner falls at dawn reward anglers willing to show up early with 6X and stealth wading.

Frying Pan River. The flats below the dam from mile markers one through seven are the main stage. Fish a CDC cripple on 6X with micro shot to keep the emerger right in the film. Cloudy afternoons are gold here — duns linger on the surface and a CDC comparadun imitating fluttering wings pulls fish after fish. A crowd management tip: most anglers leave at lunch, but PMDs often keep rolling under high clouds, so stick around.

Gunnison and Taylor. The morning spinner fall is prime — fish a Spent Wing PMD at sunrise before crowds arrive. Midday, tight-line a Two-Bit Hooker and Barr’s Emerger combo along seams. When fish move to flats in the afternoon, switch to a comparadun or cripple. Watch for pale wings hovering around 8 p.m. — the spinners often return for a second act.

Roaring Fork. From a drift boat, drop anchor in foam lines and fish a Film Critic with a Barr’s Emerger dropper on two feet of 5X. Wade anglers should work inside bends with soft hackle swings. The lower river near Glenwood fishes more like a freestone, but upstream eddies demand 6X and CDC wings. Watch afternoon thunderstorms — runoff spikes knock fish off the feed fast.

Beating Selective Trout

The pale morning dun hatch Colorado experience will test your presentations, especially on pressured tailwaters. When fish refuse repeatedly, the problem is almost always drag you cannot see. Lengthen your leader to 12 or even 15 feet on flat water, and make micro-mends of only two to three inches at a time — big upstream mends move the fly just enough to spook educated trout.

Switch casting angles before switching flies. A downstream or cross-stream presentation often solves refusals that a new pattern would not. When nothing else works, cycle through dun, cripple, and spinner patterns — sometimes trout are keyed on a specific attitude in the film, and a low-riding cripple draws strikes when a high-floating dun gets ignored all afternoon.

Weather and Conditions

Weather changes everything during a PMD hatch. Bright sun pushes trout into riffle drops — nymph deeper with heavier flies on bluebird mornings. Overcast skies are a PMD angler’s best friend because duns linger on the surface, extending the dry-fly window by hours. Wind kills delicate presentations, so shorten your leader to nine feet and add tungsten putty to emergers. Flow spikes from dam releases or afternoon storms push fish to soft inside seams — focus on the quiet water rather than the main current.

Making It Count

The PMD hatch is Colorado’s most reliable summer dry-fly event, and the anglers who fish it best pay attention to details: water temperature, cloud cover, color shifts, and the subtle difference between a dun sip and an emerger boil. Pin your PMD waters as Favorite Rivers and log every hatch session in Fishing Reports inside the FlyGuysNLies app — two seasons of entries turns observation into pattern recognition, and next year you will know the Frying Pan kicks off the week the Cheesman release drops below 300 cfs without having to think about it. Trout Unlimited’s Colorado chapter has worked to protect the tailwater flows that make this hatch possible — support their work and treat every PMD trout with quick, in-water releases. Match the daily rhythm from nymph to spinner, and you will find yourself rearranging your summer calendar around those pale little mayflies — just like the rest of us.