Colorado’s diverse river systems are home to some of the best fly fishing opportunities in the country. The hatches of mayflies, caddisflies, stoneflies, and terrestrials vary by location and season, providing anglers with different opportunities to target trout using the most effective fly patterns. Understanding when these hatches occur and what fly patterns to use can significantly improve your catch rate. Below is a guide to the major hatches throughout Colorado’s rivers, their sizes, and recommended fishing times.
Fly Hatch Stages:
Fly hatches generally occur in three main stages:
- Nymph (Larvae) – Occurs just before the hatch, offering an excellent opportunity to catch trout using nymph patterns or wet flies.
- Pupae/Emergence – The transition from nymph to adult.
- Adult – The insect emerges, providing a great opportunity for dry fly fishing.
Colorado Fly Hatch Chart:
| Hatch Species | Size | Dates |
|---|---|---|
| Mayflies | ||
| Blue Winged Olive | 16–22 | Mar – Apr; Sept – Oct |
| Pale Morning Dun (PMD) | 16–20 | Mid Jun – Mid Sept |
| Green Drake | 10–12 | Jul – Mid Aug |
| Red Quill | 12–16 | Jun – Aug |
| Trico | 20–22 | Mid Jul – Mid Oct |
| Light Cahill | 18 | Mid Jul – Sept |
| Speckled Spinner (Callibaetis) | 14 | Jun – Aug |
| Caddisflies | ||
| Caddis (various) | 10–18 | Jun – Sept |
| American Grannon | 16 | Apr – May |
| Spotted Sedge | 16–22 | May – Jul |
| Green Sedge | 12–14 | May – Aug |
| Little Black Sedge | 16–18 | Late Apr – May |
| October Caddis | 8–10 | Sept – Nov |
| Stoneflies | ||
| Salmonfly | 4–6 | Mid May – Mid Jul |
| Golden Stonefly | 6–10 | Jun – Mid Aug |
| Yellow Sally Stonefly | 14 | Jun – Mid Aug |
| Little Yellow Stonefly | 14–18 | Jul – Mid Aug |
| Early Brown Stonefly | 14–20 | Apr |
| Terrestrials | ||
| Ants | 10–16 | Jul – Sept |
| Beetles | 6–12 | Jul – Sept |
| Grasshoppers | 6–12 | Jul – Early Sept |
| Midges | 12–20 | Jan – Dec |
| Scud | 14–18 | Jan – Dec |
| Sculpin | 4 | Jan – Dec |
| Damsels | 8 | Mid Apr – Aug |
The Largest Colorado Hatches and Recommended Fly Patterns
Salmonfly
Salmonflies are one of the largest insects in Colorado, measuring 3-5 inches. This hatch occurs primarily in the upper Colorado River and offers exciting fly fishing opportunities with both nymph and dry fly patterns. These hatches last only a short time, and nymph patterns are often the most successful pre-emergence.
Recommended Fly Patterns for Salmonfly:
- Nymph Patterns: Pat’s Rubberlegs, Yuk Bug, Girdle Bug
- Dry Fly Patterns: Noble Chernobyl, Rogue River Stone, Orange Stimulator
Blue Winged Olive (BWO)
Blue Winged Olive hatches occur in both spring and fall, with the hatches being more abundant on the Colorado River. Early spring hatches are slightly larger than the fall hatches, which run smaller in size.
Recommended Fly Patterns for BWO:
- Nymph Patterns: Barr’s BWO Emerger, Sparkle RS2
- Dry Fly Patterns: Adams Parawulff, Foam BWO Parachute
Green Drake
The Green Drake hatch is one of the most significant hatches of the summer, primarily found on the Eagle, Gore, Piney, and Roaring Fork rivers. This hatch typically occurs from early July to August, with several fly patterns available for successful fishing.
Recommended Fly Patterns for Green Drake:
- Nymph Patterns: Zug Bug, Mercer’s Poxyback Drake
- Dry Fly Patterns: Green Drake Parawulff, Furimusky’s BDE Extended
Caddis
Caddis hatches begin in late June and extend into mid-summer, often overlapping with other hatches like PMDs. The Eagle and Roaring Fork Rivers are known for abundant caddis hatches. These hatches provide both wet and dry fly fishing opportunities.
Recommended Fly Patterns for Caddis:
- Nymph Patterns: Buckskin, Caddis Candy
- Dry Fly Patterns: Elk Hair Caddis, Soft Hackle Pheasant Tail
Golden Stonefly
The Golden Stonefly hatch is often less hyped than the Salmonfly hatch but is far more abundant and productive for anglers. This hatch occurs from June through mid-August.
Recommended Fly Patterns for Golden Stonefly:
- Nymph Patterns: Pat’s Rubber Legs, 20 Incher
- Dry Fly Patterns: Chubby Chernobyl, Yellow PMX
Yellow Sally
Yellow Sally Stoneflies are small but abundant, and hatches can provide excellent fly fishing. These hatches overlap with caddis and PMDs in late June and July.
Recommended Fly Patterns for Yellow Sally:
- Nymph Patterns: Oliver Edwards Yellow Sally, Beadhead Pheasant Tail
- Dry Fly Patterns: Yellow Foam Stone, Yellow Elk Hair Caddis
By matching your fly patterns to the active hatches in your area, you can increase your chances of success while fly fishing in Colorado’s rivers. Keep an eye on the hatch timing and size to ensure you’re using the most effective flies for the conditions.
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